No way would I do that. If your strapped for cash, there's better ways. The tire place I use ALWAYS has a huge stock of used tires that are cheap and they only have sets of 4 and they only sell sets with plenty of tread. I got some tires I hated once and they took them on a trade in.
If your really strapped for cash, try a salvage yard or Craigslist. I drive a lot of highway, so hydroplaning is a concern and I've sold sets of tires cheap, that weren't to the wear bars but couldn't throw water at 75mph. I grew up poor and my dad used to pick up sets of tires at the salvage yards. We lived on gravel roads and they'd get chewed up in months, not years, but they were matching sets.
Tires all have different personalities. Traction, cornering, ride, stopping, they just need to match for safety sake...