Off season rates are the best, plus you also avoid the crowds. In Florida, if you choose a time after Easter, after spring break, and before school lets out for the summer, the weather is perfect. I went one year in April, there were virtually no lines for the rides.
Some people stay at WDW hotels because of the conveniance, but many "off site" hotels are actually closer to some theme parks than Disney hotels! Others feel they have given "the Mouse" enough of their money.
Staying at a non-Disney hotel means you have more choices of meals and price ranges, and are more likely to see other Florida attractions like the Space Center, and Gatorland. At most times of the year, it's going to take about 20 minutes to get to your car and another 20-30 minutes to get back to the hotel. But, meals are cheaper away from the theme parks, and you can take a swim in the pool and maybe even a nap at lunchtime!
Off-site hotels in Orlando and Kissimmee often offer rates as low as $59 per night plus tax, while Disney prices usually start at $99 in the off season. (I've had unconfirmed reports of rates as low as $36 per night.)
Definitely try the big travel Web sites to search for the lowest possible price. There are also a few specialist Web sites like Mouse Savers which list all kinds of discounts at Disney area hotels and resorts.
The Radisson Resort Orlando - Celebration has "preferred rate" specials for Disney Fan Sites/Information sites such as WikiAnswers. Click on "RadissonATDisney's" Bio page for an introduction to this resort, located only 1.5 miles from Disney World and a link to their site with these rate specials.
Just a note:
It may seem more expensive to stay in a WDW resort, but there are a lot of transportation benefits to consider!