Wonderful question! I am a Disney World Cast member and am very happy to assist you with finding an affordable hotel near Disney World. If you are looking to stay on property the lowest priced locations will be the Value Resorts. The on site property with the lowest rate is usually either Disney's Pop Century Resort as well as Disney's All Star Resort. These two generally start about about $100 per night. The great thing about staying on property is that you will have access to Disney's Magical Express which will get you to and from the airport at no charge. This is a savings of about $65 each way which is what you would pay for a taxi. You also get access to the parks for Extra Magic Hours. This makes it easier to get one those rides that you were not able to get a Fast Pass for. Speaking of Fast Pass', you will be able to book Fast Passes 60 days in advance when staying on property as opposed to 30 days out when staying off property.
If you are looking for an area off site then you generally find the lowest priced hotel rooms on U.S. 192 in Kissimmee. Its within a few miles of Disney property and most locations in the area will have rooms at under $50 per night. Prices will vary by season, and you will usually find the lowest rates in the winter. But dont worry you will be in Florida and winter will still be quite warm. One thing to keep in mind is that if you are staying off site you will need to take a taxi to you your hotel from the airport, but the good news is that most of the hotels will have a shuttle to get you to and from the parks.