My ds is currently concluding his term and I've made several trips to the area during his stay. Yes, the Sheraton Vistana is the closest but if you can't find a good deal there you have lots of other options. The Holiday Inn Sun Spree is immediately across the Hwy. It is important to know when looking at the area that SR535 is also known as Apopka Vineland Rd. The address of the nearest business (Walgreens) to the apt. complex is 13502 S Apopka Vineland Rd Orlando, FL 32821. You should be able to use that to run a search for any hotels you are considering to see the milage. There are so many options and price ranges that I'm not sure how to advise you. If you are looking for real economy rooms you might want to consider the East end area of 192 (also known as W Irlo Bronson Memorial Hwy) the addys with numbers in the 4000s-5000s range would be easily accessible. If you wanted higher end accomadations you might want to consider Downtown Disney (Hotel Plaza Boulevard addys) or Palm Parkway addys would not be far removed. The very southern ends of International Drive would also offer up some quality rooms. And of course you can't beat the quality of the rooms on property (though I wouldn't waste the extra $$ for this event). Even the lowest rate Disney resorts are not more than 10-15 minutes from the property.
If you have questions about a specific hotel/resort I would be happy to give you my opinion on the proximity and appearance. Good Luck to you both and if I can help out just ask.