I vote against it. I'm with 4merper4mer in this one. I don't enjoy sleeping in someone else's urine or fecal matter that has been dried up and crusty on the bed.
Keep a look out for mattress stores and sales. Usually happens all the time.
You'd be better off going to a mattress store and asking to buy the floor models if yiur looking for a cheap fix. Much better than piss, s%#t, puke, bed bugs, dust mites and who knows what else is out there.
Or you can buy the ised ones. Chances are, they are cleaned an alright. But that's just me. I wouldn't.