If you're in the Tampa area and already did a boat dive, I'd say there are two big options (which folks have already mentioned!):
Option 1: Shark tooth hunting. Drop down to Venice and go looking for megs and other fossil shark teeth. I love Aquanutz but they tend to book up fast - it's a three-tank charter, and they let you dive your tank all way the down to 500psi. In thirty feet of water. I was down seven hours underwater this week with them, love that they let you do that - we left the dock at 8am and didn't return until 6pm. Found one big partial 3/4 meg, and tons of little teeth, a little less than normal.
Option 2: Freshwater springs/caverns. There are three main "types" of freshwater springs diving in Florida: open water basins, caverns, and river/drift. There's a
good map here. If you liked Blue Grotto, and want to check out other open-water safe caverns, head over to
Paradise Springs (requires AOW; $30 cash only) or Ginnie Springs. You already said you weren't interested in Devil's Den - the underground entrance is fun, and the swim-throughs there are a LOT of fun, but if you aren't into swim-throughs, you might give that one a pass. Try to avoid all those places on the weekends if you can.
Fun open-water basins include
Manatee Springs, Fanning (very shallow, I'd prob skip that one), and Orange Grove Sink (kinda far for you, and vis right now isn't the best) - all state parks, so very low cost. Unfortunately many of our good open water sites are still flooded (Troy, Royal) from winter rains.
And finally there's the river/drift diving. The Sante Fe is low and clear enough right now that you can do a nice short (~10-15 minute) drift from Devil's Run down to the ballroom; be sure to bring a dive flag if you do that. And of course there is Rainbow. If you want to do Rainbow, the cheapest way is to use the
Rainbow River Water Taxi. Give him a call ahead of time to confirm that he is available for the dates and time requested, and he can give you his current prices. You will drive to KP Hole, meet him on the pontoon boat at the dock, and he will ferry you upstream and drop you for about a 45-90 minute drift (depending how fast you swim). You exit at KP Hole where you boarded the boat.
If you don't want to arrange the taxi yourself, you can also book a guided dive with one of the operations that brings their own boat (Bird's Underwater and American Pro Diving both run trips with their own pontoon boats out there). In that case, you usually meet them at the shop and go from there, they will have everything arranged.
You have a buddy (which is great; almost all the freshwater springs require them), but it's pretty easy to hire a
local guide around here for guided tours, and we are blessed by a large number of
great dive shops where you can rent tanks, gear, etc.
Option 3: Scalloping! Okay, this isn't scuba diving, but it's really fun and the season just opened. It's all on snorkel in about 3-5' of water. You go out in the gulf and collect Bay scallops - there's a limit per person and per boat. It's great fun, esp if you like seafood (you get to keep and eat the scallops; there are also places that will "cook your catch" if you don't have a kitchen where you're staying). I like
Bird's Underwater for scalloping trips personally.
