Skeet - it all depends on the size of the pontoon boat and what you're driving on. South Florida Diving HQ's runs a pontoon boat, but it's 45' long. That's kinda like what they run in Key Largo too. Tons and tons of room, and certainly seaworthy enough for any seas they might go out in - if it's too rough - you just flat don't go out. I guess in Texas they call that a dinghy...
The smaller pontoon boats are nice and flat and perfect for protected waters. We never ran any of the fancy pontoon jobs with things like heads and padded seats - we just ran big flat gear and passenger platforms.
They maneuver like bloated pigs in the wind, but I always kinda liked it like that - it made things interesting and also meant that no one else could drive the things in bad winds.
On one of the pax pontooners I drove with twin outboards, we had one go out for a week, and driving that thing into the wind with one engine was a real exercise in seamanship.
I guess we sorta forgot to tell the Coast Guard that we were short an engine for week, so we also got a $250 fine from them. Not sure why they bothered, but I think they didn't like the company owner that much. Politics.
For afforability, you can't beat a pontoon boat - it's just two aluminum hulls bolted to a platform. If your waters are calm enough, go for it.
If the weather stinks, stay home and have a few drinks; if the weather is fine, then go have a great time.
Now I need to make a plug here for an interesting company called Wilson Distribution:
http://www.plasticpontoon.com/index.html
These guys make plastic pontoons, and they're damn nice too. I looked them over at length at one of the trade shows and really liked them. They're tough, pretty cheap, and a great way to make an AWESOME dive platform without a whole lot of work. The people at Wilson were nice too, and I'm sorry that I just could not do business with them. Maybe one day.
You could probably make one truely righteous floating condo out of three or four of these things bolted in a train on a quadmaran? hull. The zoning people in Boca Raton would have a universal coronary at the sight of that though.
Sun Tracker would be ok and trailerable too.