Head over to the Orlando Hotels and Attractions Board and check out the threads on SVV and SVR. There is more information about the larger SVR resort, but SVV is no slouch. It was the first place we stayed when visiting Disney (through Air Canada Vacations many many year ago) and is a great option. Maybe 15-20 minutes by car to the parking lots of the Disney Parks, only 10 minutes to SW and 15 to Universal. You can't get a better location, and MUCH more luxurious accommodation than all but the most expensive Disney rooms. A suite the size of a 2BR at Vistana on Disney property is generally near $800/nt.
SVV sold us on staying off property and led us to eventually buy a Timeshare (resale) at the Sheraton Vistana Resort, but it was all based on our excellent experience at SVV. I can understand why Costco is offering stays at this excellent property; it matches perfectly with their best bang for the buck market.
To echo Spiceycat's point though, policing in Orlando (actually pretty much everywhere I go in the US) is much more visible than here in Canada (except maybe Montreal). DUI is not tolerated, so be sure to be careful with consumption or take the shuttle. SVV offers shuttle to the parks, probably free under the Costco package; they do charge $9/pp for timeshare owner stays, but I wager that Costco has made sure that the park shuttle is free for their bookings (read the fine print).
You can't do much better than this, especially if the price is right!