In the 40-60K range you'll find quite a variety of suitable boats. Catalina 30,34 and 36s can all be had in that range, but to get one of those with the transom cutout may be more difficult. The MKII versions have the best cockpits and swim access but go for more than that in the larger sizes. Also, an early Catalina 320 might be had at that price. The Hunter Legend series 33.5, 35.5 of the late 80s early 90s have good layouts and could be suitable for coastal cruising that you are contemplating. These open cockpt models allow the best swimming access, but a good, deep stern ladder can make most boats perfectly satisfactory on that score.
Depending on what age you're prepared to go to will also impact your selection. C&C, CS, Sabre, Cal, and other once-prominent brands could well fit the bill too.
The big adjustment for you will be the departure from trailer sailing. Hauling a keel boat 'between trips' may not prove feasible or practical. You'll lose that flexibility to easily/inexpensively travel from Maine to the Keys.. and may have to choose a narrower sailing venue.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"