I have done the drive between WDW and St. Pete Beach many times, following I-4 to I-275 and exiting I-275 either at Gulfport Blvd. (22nd Ave S) or at Fl-682 (54th Ave S). There are no tolls if you use Gulfport west to Pasadena Ave and cross the Intracoastal Waterway on the Corey Causeway. If you use the exit further south at 54th Ave S, you will pay a cash toll on the Pinellas Bayway. I forget the exact amount, but certainly less than $2, perhaps $1.25? The latter route takes you onto St. Pete Beach near the Don Cesar at the south end of the commercial strip while Corey Causeway brings you onto the island near the north end of the commercial strip. We stay at the TradeWind Island Grand and find paying the toll is more convenient route than following Gulfport Blvd.