Unlimited rights, assignment of Copyright - Creative work is priced according to the cost to produce it and the amount of use the licensee wants. Some photographers say they don't charge for the production but only for the usage and others will charge for the production and allow unlimited usage. I take the middle ground and charge for both. A National company will be familiar with paying for each type of usage, but they will still fish for photographers that will work cheap and give away the farm. There are forms for the different types of usage (web, print, tv, billboards, magazine ads, Op/Ed, corporate internal communications, bus stop ads, trade show booth art, etc) to help you develop a standard pricing structure for licenses. Check out the PFRE Flikr forum and search for Ashley Morrison. He frequently posts a link to a "BUR", a Basic Usage Rate form. It's a good starting point that shows how the creative industry commonly breaks down separate usage line items. Another aspect is time; licenses are generally specified as being valid for a set period of time for new uses, printing runs, TV ads. Each additional usage or time period has value.
A National company may use images in a wide variety of ways for many years. Chances are that if you create some images for them and hand out an unlimited license or assign them the copyright, they won't need any new images for several years by which time they may have forgotten all about you and you won't be getting any repeat business. On the other hand, if they need to renew their licenses on a yearly basis or when they want to put the images to different uses, they will contact you and you may get additional new work.
With RE work we are typically selling a license good for between 1 and 6 months, the life of a listing contract. It might run longer for more expensive or unique properties or if the market is slow. The usage is usually limited to selling the property with no restrictions on media type or region. I also allow the agent that contracted for the photos to use them to market themselves after the home has sold or they are no longer involved. They do not get the ability to transfer the images to any third party for a fee or free. An agent taking over a listing has no license to use the images provided to the first agent without purchasing a new license. This packaging of licensing makes it easy to market to RE agents that are not used to working with the Creative industry. Their usages are very clear cut and it's futile to approach them with an ala carte menu of licensing options. They might find it too complex and forgo using you.
Pricing per usage is completely up to you. I would suggest that you not be shy about asking for what might seem like a lot of money per image. $1,000 per image/year might not be out of line if they intend to use the photos in their advertising (not exclusively for listing a specific property). If they were to print 10,000 brochures, that's $.10/image/brochure. On their web site they may get hundreds of thousands of page views so an image might only be costing them $.001/view or less. The images may also wind up in many other places making their cost per use vanishingly small even if you were to charge the $1,000/image. For a total buyout of your Copyright, you will want to charge even more. It's not outrageous to quote $25,000 for 10 finished images. A large company is going to use the images you make for them to generate millions of dollars of business so don't feel guilty.
If you haven't scared off the client, they may come back to you for a quote on only the usages that they really need, so the BUR form I mentioned above is a good tool to calculate your licensing fees and re-figuring them agains consistently when the customer wants to talk options. Whatever you work out, be sure you have the rights to use the images in your own portfolio in writing.
Last but more important, register all of your images with the Copyright office before you submit them to your client. Don't pick and choose, it's the same price to just submit all of your raw work at the same time. You will have a tangible piece of official paper to convey to your client if they really do want to buy out the copyright.
Travel - I provide around 20 images for each RE job as my standard service. Each image takes about 6-7 minutes to shoot, process, deliver and bill. That's roughly 2 hours per job. I know what I need to make to break even and I know what I want to make to reach the goals I have set for myself. I made a chart of the surrounding area, it's a fair sized service area but low density, and I can estimate how long it takes to get to each region. These regions are outlined on a map with 30 min travel time lines like a topographic presentation. When I get a request for a quote, I take the bare photography price and add the travel time/mileage charge from my region map. I charge the same for my time whether I'm making pictures or driving. There is no sense in taking a job two hours away and billing any less just because I'm behind the wheel. I could do 2 more local jobs and make more money. I will happily drive as far as a customer wants to do a job if they are willing to pay me for the service. Strangely enough, I've only had one job in the city where I live. The agents here seem dead set against using professional photography. One told me that the ONLY reason she takes any pictures is due to the MLS requirement to have one of the front of the house. I can get from one end of town to the other in 15 minutes or less, so I don't charge for mileage here in town. I offer a substantial discount for jobs in town as I can eat lunch at home and do a few errands while I'm out running around.
It's easiest if you can offer a total price for each city you service with your travel expenses built in. Agents will then know that if they want you for a job in City B, it's $XXX, City C, it's $XXX. If they have to find the distance from your office/home to the listing, they won't because it's too much work. If they can just look at your pricing page (if you have one) and can see that City B is priced at $XXX you won't get calls to quote every property individually and they are less likely to try and talk your price down. People will dicker over a stated price but they are far less likely to want to negotiate if the price is written down. Something I learned from from other business people I know. They advised me to always provide a written quote over telling a customer a price over the phone. They were right, when I started faxing (yeah, I'm old) quotes out of my accounting system, I received more orders with less negotiation. (This is in the USA. Other parts of the globe are far different).
