Hi,
I had planned my first solo trip for 12/01. However I was hospitalized with pneumonia which extended into the trip which I had to cancel. Can't tell you what a bummer that was. However, My mom (mid 50's) and I (early 30's) decided to go to WDW and IOA in 12/02 (about a 10 day stay). I love my mom, but had enough by day 7. Like Simba's mom, I don't think that its selfish for me to go on vacation by myself as I work hard all year long. So this Dec. I am finally going solo however, like you I need to watch my money.
Last year, we decided to do everything so we spent a ton and we had to cut corners where we could. First we decided not to stay onsite at Disney (even AS in offseason is still about $60 per night). I looked into Priceline and decided to go that route (which for my first time was very easy). Priceline has a sister website called biddingfortravel.com. When you enter the site, scroll down the first page until you come to FL - Orlando/WDW and then double click on that title. Read the first two threads that pop up as they tell which hotels frequently accept the bids in the Orlando area (make sure to click on and read the reviews for each hotel in the level you may want to bid on) and also will answer general questions. All the other threads are post of what people have won for their bid, date of stay and amount for same. Last year I bid on a 3* in Kissimmee. This hotel frequently accepts bids for $35 per night. I left a review for the Renaissance World Gate (we did not have a bad stay, but some people have had not so great stays due to conventions). Hotel was clean and we did have a good time; however, I would suggest that you get a rental car a so you can come and go as you please. (You can always attempt to rent the vehicle on Priceline to.)
Just remember if you decide to bid on Priceline you are bidding on any hotel that comes up under that level. For instance, the resort level for the closest to Disney property includes the Hilton (DTD), Wyndham (DTD), Swan, Dolphin, a Marriot and one or two other hotels not located on Disney prop (bids usually accepted from $60-$90 per night). However, if you bid $60 per night and Priceline accepts, they can place you at any one of those hotels. You may get lucky and get one of the DTD resorts or you may end up off property at a nice resort such as the Marriot Orlando, but would need your own vehicle to get around.
Lastly, several sites such as this one post when hotels are offering their rooms cheaply. Also check occasionally with mousesavers.com to see what type of onsite room discounts and other preferred hotel offers she has. Okay final option. If need be, cut your vacation at little short. If you wanted to do a week stay, try a 4 night stay instead as it will be a little cheaper and as this will be your first solo visit anyway.
I hope that you get to make it there and have a great time by yourself.