So glad you changed to the regular hotel room. That's another big savings for your trip. Have you ever looked at Mousesavers web site? There are many terrific ideas and I am sure you can find many more ways to save!! If you want to pretty much eliminate your cost for transportation to the Pop Century, consider taking the bus. It looks like it would only be about $2.50 for both you and your son. (It only takes about an hour and a half! I've been on the Mears shuttle for much longer than that!)
All the information for this is outlined on Mousesavers, in the Getting to Walt Disney World section!!