Hi cguill....
We are timeshare owners there. I think they rent them out for like $150 for a one bedroom--$180/night for a two bedroom. But I wouldn't rent directly from the resort. Either try and rent from an owner (check out sites like TUG
Or try this site (they offer specials). Just try and be sure you are getting a newer or remodeled unit. In a 2 bedroom, you should have one king bed a double sleeper sofa and two double beds (not singles).
http://allears.net/acc/faq_svistana.htm (check out the no housekeeping rates if u don't mind not getting housekeeping).
Other places to check for rentals :
http://www.redweek.com/
http://www.myresortnetwork.com/
http://www.vacationtimesharerentals.com/
http://www.vrbo.com/
http://www.skyauction.com/
You could try calling Sheraton Vistana directly and asking if they are offering any sort of specials if you attend a timeshare presentation. They usually last 90-120 min and can use hard-sell tactics, but not always. I've read some people found the presentation fine and got a great rate just for attending.
Hope all this helps !