I'm vacationing at Sanibel right now and have been coming here for about 15 years. We're staying at Sanibel Siesta (SS), next to the Holiday Inn near the intersection of East Gulf Drive and Donax. This is our third year here. It's RELATIVELY cheap as Sanibel goes. You could easily spend $400-500/night for a 2 BR condo on the island. We're paying about $250-260/nt for a 2 BR, back from the beach. Beach front are substantially more expensive. Buildings # 1 and 2 are well back from the beach (a 1-2 minute walk if that), but they are the only ones that have an elevator. SS has few amenities except it does have a nice, heated pool and the condos are neat and clean. Plus it's right on the beach. The Holiday Inn is next door with food and drink if needed. Business is a little slow, so I'd call them directly and try to get a discount. We did for this stay, but January is a bit slower then later in the winter. April is considered high season, at least the early part for sure.
I stopped by Dean's a couple days ago with a gear question and to check them out. Nice, professional appearing shop. They were quite helpful. Apparently they support the local public service divers as the shop was full of deputy sheriffs and their gear. That's speaks well in my book.
I've not dove out of FT. Myers, but I understand this it's a long trip and marginal sites. Normally I'll run down to the keys for a couple days of diving when I'm here, but not this year. We've got some g-kids here and they take up the time-not a bad thing.
PM me if you have any questions.