Would everyone agree that for starters any 30 plus year old boat that was going to be used the way the OP plans should have the following done if it has not been done in the last 5 years and good evidence that it was done right.
1. Drop rudder and inspect and or replace bearings and all linkage.
2. Replace chain plates
3. Replace standing rigging
4. Replace running rigging
5. Check ground tackle and get spare
6. Check sails and get spares
7. Check electrical and make sure lights, pump work.
That sounds like 10k minimum assuming some of the above is OK and some needs doing.
The key phrase there is "If it has not been done in the last 5 years" If it hasn't, then that should be accounted for in the price of the boat.
This is where a GOOD surveyor is worth his weight in gold.
In any event, any boat that needs everything replaced is likely not a candidate for the OP anyway.
This is where an argument could be made for the purchase of a freshwater boat. A clapped-out, bearded hull Oday 32, for example, might fetch 12K in Florida. The same boat on Lake Michigan or Lake Erie might fetch $15K. even figuring in the cost/time to transport, the fact that the freshwater boat will be in arguably better shape with no saltwater exposure and half the in-water time could make it the cheaper boat. Sails, rigging, rudder, will have half the cycles and sun exposure of a saltwater boat, and the bottom will likely be in much better shape.
There are lots of $15-20K boats out there that will satisfy the OP that don't need $10K worth of work.
The problems arise when one buys a $35K boat for $20 K. If it sounds too cheap...it is.