www.craigslist.com —-though you want to do some research on exact models to make sure you’re not getting ripped off.
I work at Micro Center…you can find pretty cheap TV’s there too….42“in for like 799.99 after rebate of 100….I have a Sony 37” for like 839.99 as well. www.microcenter.com you can check some prices if you happen to be near a micro center store.
If you are buying used, try and talk the person down in price…do some research in advance to know the retail value of that TV and if they are asking anywhere near it, use it’s age and time used as points to talk him down. If they are trying to sell you a warranty they had already bought, tell them to pro-rate the difference on the warranty and they can keep it.
If you need any more help let me know.