A lot of good advise posted above and here's my $0.02 worth.
"A boat should drink 6, feed 4, sleep 2"
or something along those lines.....(read that here I think)
Assuming you and your partner take 1 cabin for yourselves and then have a pullman or something for guest(s) OR use the salon setees for bunks, you can probably get away with something in the mid 30's. As for pricing, that's a whole separate can o' whoop-azz.
You've got to consider the following factors as having an impact on (what appears to be on the outside) similar boats.
- Level & quality of maintenance to date
- Condition of the hull (Been grounded, Blistering/Osmosis, Needs Paint ?)
- Condition of the sails, rigging etc and what're you getting ?
- Condition of the mechanical items aboard (engine, plumbing, wiring)
- Additional equipment included in the sale (electronics, galley etc)
- How desperate is the owner to sell & just as important WHY
Good rule of thumb is to plan for boat price + 30%-50% (additional equipment, repairs, getting it "right") Also, don't forget that blue water sailing assumes some general wear & tear on the boat daily. This will require ongoing maintenance and we all know that even if you do the work yourself, it's still not exactly "cheap" just cheaper....
Also, don't forget to set aside money to live on while cruising. I'd budget your monthly expenditure to be the same as it is on land, but you'll be spending it on different things. If it turns out less, then GREAT but don't plan on necessarily saving money while cruising and it'd really suck if you got the boat but had to cut the trip short cause you ran outta $$$
Looking at Yachtworld.com would be my suggestion. Put in your price range and a size from 30-40. See what pops up. You might get lucky but the budget you mentioned is tight on a good day...