$1500 for an older Catalina 22, O'Day 23, etc. that's in sailable, but not "pristine," condition may not be unreasonable at the end of this season. I think you may be hard pressed, though, to find one for that price that includes the trailer. I'd suggest trying to stretch your budget a bit, too. Start looking now, but take a few extra months and save a few more dollars. If you find something now that's in your range, great! But if you can get to about $2000-$2500, I think you're more likely to find a decent boat that won't need a whole lot more than elbow grease to meet your needs.
I'm a "budget" buyer, and I can appreciate that some times you're willing to spend $1500 now for a boat, even though you know it's going to take another $3000 to fix it up, because she's in sailable condition now and the other changes/enhancements/etc., can be done incrementally. That's the approach I've taken with both of my boats. But, I have to tell you, it's amazing how much an extra few hundred dollars gets you; it is disproportionate to the actual value of the work/equipment the current owner has put into the boat. You'll probably see a 1.5-2x multiplier, and possibly more.
The best time to buy a boat is when nobody else wants to buy - that's at the end of the season. If you can hold out that long, you'll be even more likely to find something in your budget. No, you won't be able to SAIL it for too long before it gets too cold, but, on the plus side, you'll have several months to handle some of the repairs/maintenance before she's back in the water. Personally, I'd MUCH rather buy a fixer-upper at the end of the season and work my butt off all winter fixing her than to buy her in the spring and "waste" the spring and part of the summer trying to get her ready.
Anyway...welcome to Sailnet! You'll get lots of opinions, and lots of suggestions, and some might even be useful!