You want a bargain, buy this boat:
S2 7.9 racer/cruiser sailboat
Sorry, I have no affiliation, but honestly that's a bargain basement price.
Truth in posting... I own an S2 7.9... if you stretch and buy that boat over your $6000 budget, you can thank me later for getting you into a boat that is both safe to learn on, great to sail fast, and even better to take your family/friends out on.
Just thought I'd scour the craigs near you.
if you consider that boat, bang the deck near the chainplates (where the stays attach port and starboard)... bang it with a box wrench or something, working your way out, listen for THUD (that means wet core)... BANG means solid.
Do the same for the mast step.. check that the mast step is level (lay a 2'x4'x18" across the width and length of the step, if it doesn't deviate more than 1/8" the mast step is probably dry)...
Check the rudder, and the cheek plates (alum plates the rudder sits in and connects to the tiller)... make sure the hole is round...
Look at the bottom for blisters (bottom will have what looks like large zits)... the early production years 1982 and 1983 (that's a 1982) were more prone to these (not the end of the world, but would be work to fix)...
Also lastly, that's the BMW inboard model... make sure it runs! Getting parts for the BMW inboard is tough these days, but one that runs and looks clean/cared for, should hold up (we have 2 in our club)...
The S2 7.9 is nicely trailerable, but is also stable with daggerboard up. I think others here will testify, its a better boat than all three you mentioned.
By the way, that Lancer looks like a decent boat as well, but its on the large side for "trailerable." I have a friend who did it for years with his, but even he would admit that he only ever would want to trailer it twice a year. The Oday 25 is easier than the lancer, and about the same amount of work as the S2 to launch, however the S2 is slightly easier to get in and out of the water, with both of them about the same for raising the mast. The S2 is an infinitely better sailing boat though.
If that S2 is structurally sound at that price, it's a bargain, they still draw about $10k or more, boat/motor/trailer... Especially if the sails in his pictures are in any kind of shape.
Also if you buy the boat (and you should put that one at the top of your list - for the others here, I couldn't find a bargain Cat 27 near him, which I'd agree is a nice starter cruiser), consider joining the S2 7.9 association, they basically warehouse all the owners in 1 place, and there are resources from everyone there that can help you find replacement parts, and how-tos to maintain the boat. Nice people. http://www.s279.org
By the way if you were talking about THIS Oday 25? http://houston.craigslist.org/boa/5042139926.html
That's actually an Oday 26, and even the Oday 25 is 4100lbs, not 3850, the Oday 26 is 4800... I'd say that the Oday 26 is a slightly better boat than the Oday 25, but you MUST look also at the mast step on it (same way as I stated above)... the Oday 26 is prone to rot under the mast step (as is the S2)... the layup is trickier to repair on the Oday though.