a quick tip is narrow the decade of year built you want...it helps narrow down design parameters, 70s,80s, 90s 2000s etc...
what kind of racing, and what kind of cruising?
60s? you could say a cal40
70s any pseudo ior boat, I36, yankee38, cals, pearsons, ericsons etc
80s and 90s and 2000s a benetau or something?
countless boats out there that fit this "criteria"
for 50k I would look at catalinas, benetaus, kitted I36's or ericson 37s and similar that will get you you max out of your budget