Coastie, it sounds like you have a challenge ahead of you. Buying the boat is the easy part.
Having said that, there are benefits to owning your own boat. You set your own agenda including the departure/return times, where to dive and how to dive. Screw the cattle boats.
I recommend a 24 foot cuddy cabin/ single bridge with inboard/outboard and V8 engine. Galvanized trailer with electric winch a must. The boat should be fitted with a stout teak swim platform and ladder, stainless steel. Get the usual CG safety gear, compass, fenders, 300 feet of 1/2 inch braided (not twisted) anchor line, a 12 pound Danforth anchor and a grappling hook. You'll need a chart recorder, radio and GPS, plus charts. Find a boat which has fairly low freeboard. That probably means a hull with liner and free standing motor housing. Look for companion seats which have storage capacity. Check under the bunks for additional storage. You need a lot of space for tools, PFD's and spare parts kit. The fuel tank should hold at least 60 gallons. Look for two windshield wipers, or install later. Keep an eye out for a tank rack of some kind. Also, think about building a simple tank cradle from PVC tubing. Check for two LOUD horns. Figure out a stowable mast for a dive flag. A collapsible boat hook can be doubly useful. Get one.
Learn to use your radio and other electronics. Keep a separate VHF or weather radio at home. Learn to interpret the forecasts. Also, use the internet to access NOAA reports.
This boat will have a max capacity of 4 divers and gear.