I'm not a fan of used tires. A) they're old, so the rubber compound and the internal belts and structure are aging. B) They've been run in an unknown direction, causing the belts and structure to sort of settle into a certain "shape" if you will. So you pop them on, and start driving on them, and you probably aren't going to get lucky and have them rolling in the same direction they were previously run in, and so pretty soon you get tires that won't hold a balance, hop and cause the steering wheel or your seat to vibrate, and in extreme cases, will actually break a belt internally, and have a bulge...and maybe even blow out, especially in summer heat on hot pavement.
IMO, spend your money once, spend it right, and buy a decent set of new tires. You don't have to go out and get Michelins or Toyos for $200ea, but in the 15" "normal" tire sizes, I'm sure you can get something nice for between $75 and $100ea. Read your specs (why I like
www.tirerack.com) and purchase something with a high tread wear rating and a quiet tread pattern with good side venting so they shed water well and don't hydroplane, and you'll be very happy with the purchase. They'll last you years if you rotate them every 3,000mi (front to back only), get a front end alignment done at time of install, and keep them aired up properly.
Tires aren't a waste of money. They're an investment in safety and vehicle longevity.