I think I might have the perfect low-cost solution for you.

Right around the corner from St. Pete Beach (only a mile or two) is Tierra Verde. Just down the road from here is Ft. Desoto Park, which is actually an island in Tampa Bay that you can drive to. This is a absolutely fantastic place to fish for many species cheaply. The island is shaped like the letter "C", so you can surf fish the outer beaches or fish from one of two piers OR you can rent a canoe and fish the mangroves on the inside of the island. Lots of different species can be caught here including redfish, seatrout, snook, tarpon, pompano.......just about anything really. There is a bait shop in Tierra Verde called the Bait Bucket where you can get a temporary license and any artificial or live bait you need. There is a fee to enter the park, which is a really neat place to check out whether you fish or not. I recommend using live shrimp under a Cajun Thunder bobber or a Mirrorlure if fishing the mangroves. Very possible to catch some nice size fish here. Great beach here as well. Hard to beat this place. Here's more info:

http://www.pinellascounty.org/park/05_Ft_DeSoto.htm