Prices are going to vary wildly. You should decide a few things before looking for a rental:
1) What is more important: price or location. The farther away you get, the lower the price, generally. We rented a 5 br/4.5 ba in January for $130/nt including pool heat from an owner on VRBO.com. It took about 25 minutes to get to the parks with no traffic. The house was located in Davenport, off of the 27 just south of the 192.
Here is a map that shows some of the subdivisions:
http://www.orlandorentalvacations.com/Location-map.htm
2) Do you need resort amenities like a community pool, gated community, etc? You will probably pay more to stay in a development that has these items.
3) Is room configuration important? Most 4 br houses have two bedrooms with king/queen beds and two bedrooms with two twins in each. If you are traveling with more adults than kids, you may want to look for someplace that has a different configuration.
4) Is is important that there is a theme bedroom?
Once you narrow down what you are looking for and what communities you are interested in, you will still get a wide variety of quotes. I just went through this process to rent a condo in January. Quotes for 3 br condos in the same development varied from $735 to $1341 for 10 days. Read the reviews, decide on a reasonable price, and go with the place that best suits your group's needs and an owner you feel comfortable with.
Good luck!