For the older boats, you're not buying the boat, you're buying the owner. I bought an '82 Pearson 32' which was treated like a shared heritage (it's the last hull laid). I have all the original manuals, decades of maintenance records, and I'm continuing the tradition. It cost me $20k, but I've put close to that into it and I still don't have radar or solar. When I was looking, I found 3 boats that had owners who were clearly over the top in their maintenance, had added many enhancements and treated it as a labor of love. I bought one of those boats/owners.
I would also suggest that a newer engine and sails (or replacement) be part of your plan. My engine had 450 hours. Look for engines which are slightly overpowered for the boat size and with under 900 hours. The sail set you'll have to decide for yourself based upon usage.
A quality surveyor is a must, and spend some hours finding the right guy. I looked at the surveys for a bunch of boats I didn't buy, and after I found what seemed to be the right guy, I checked with other owners, a boat yard, and a broker to confirm my decision. I spent $$$ on two surveys and backed out of the first boat, because the surveyor saw things I didn't.
Reserve 20-40% of your budget to upgrade things you Really Should Have, and I'd put modern electronics in that category for offshore use (SSB, GPS, radar, GPIRB), but there are experienced sailors who do without those.
Finally, if you're sailing in the Sea of Cortez you can buy boats cheaply Down There. Check out Latitude 38's Classy Classifieds
. However, you should know some people down there who can help you find the right surveyor, boatyards, etc. You may have to spend a few weeks on site to avoid making a mistake.