Buying a used sailboat
Years ago, my father and I were constantly looking for a "Good Used Boat" in the range you describe. We always used a guide line that a G.U.B. should cost about $1,000 per foot. Anything less would probably take the difference to bring it up to standard.
A few years ago, I purchased a "Fixer Upper" at about half of the $1k per foot guide and have expended a good deal of time, money and effort to bring her to the G.U.B. level.
I have been involved in boats for 35 years, and spent a number of years as a rigger at a marina, so I knew what I was getting myself into.
The $5,000 25'' boat that needs "A little TLC" may knock you for a loop. Older vessels have blistering problems to deal with. Not to mention all the systems, through hulls, rig etc. As far as a wood boat is concerned, the knowledge, cost, and maintenance can humble even the most wealthy individuals.
If you find what could be the perfect boat, you still need a survey by a qualified Marine Surveyor. No insurance company will touch an older boat without one, and YOU need one just so you can have a list of all the "Projects" you have ahead of you.
I have 1 year to go in my projected 5 year time-line to bring my boat up to fully found condition. It has been a labor of love for me, and I wish you all the luck in the world, but proceed with caution and beware the deal "Too good to be true". There can be rough waters ahead for you.
I agree with sailmc, get a smaller boat, learn the ropes, and then get into your project with eyes wide open.