Going from the TTC to USF takes 3 busses, and really isn't worth it because of the time involved.
If you're going 1 way switching hotels, then I'd say yes, make it an adventure and save some money.
Going from Disney to USF using a towncar service is approximately $30 each way (3 people), plus tip, slightly higher for Mears.
A few months ago, we (board users) looked into the 3 busses from the TTC to USF and here is what we found. This may be outdated, but you get the idea.
"At the TTC, board link #50 at 8:48 a.m. . Deposit $1.25 (exact) for each fare and ask for transfers. Arrive SeaWorld at 9:09 a.m. . Transfer to link #8 departing SeaWorld at 9:23 a.m. . Arrive intersection of International Dr/Kirkman Rd. at 9:44 a.m. . Transfer to link #37 northbound on Kirkman Rd. at 9:48 a.m. . Arrive Universal at 9:57 a.m."