disney visa (0% financing for 6mos, plus depending where you apply for it you'll get disney cash which you can use down there).
If you have any walking issues call randy's mobility and rent a electric scooter...you'll stand in a "priority" line for any of the disney bus transportation to the parks and downtown...plus MOST rides have a special entrance too which enables you to get on and off the rides much quicker than standing in line (learned of this due to sons leg injury).
As for room discounts with only one I doubt you'll have much luck find anything "cheap", but Pop century has a bit cheaper room tax compared to other on property resorts because they are on the border. Plus they are more centrally located to the parks and don't share transportation with other resorts when going to parks. Buses run approx. every 10-15minutes but will definately save you car rental costs.
There's may forums that will give you tips on saving money and info about current promos (the best promo I have yet to use is the free dining which I always upgrade for the few extra dollars per day to include a table service meal...always nice to have a sit down meal after a long day).
Here's a few links to read over if you've never been or have time to plan it out...
mousesavers, allearsnet, laughingplace, and passporter.net just to name a few.
and if you end up staying off disney property you can buy tickets from undercover tourists (they offer discounted tickets from time to time).
ps. if you want a fridge in the room and have any type of medical needs for say insulin they'll give you one in your room without charging you for it. Makes it nice because you can always keep a bottle drink cool to take with you in your backpack to start off the day..and if you purchase the flavor packs and are on a tight budget you can stop at a fountain and refill it with water and toss in your flavor pack to stay hydrated.
