You need to be careful as they are generally very worn out and sometimes munch tapes. If they are worn you get bad quality, if it munches, you get ruined tapes.
The VCRs from Goodwill suck. I bought one for about $4 and used it only twice before it ate a tape (luckily, not an important one). I used it once more to record some of the analog stations shutting off and then it ate a part of that tape too. Suffice to say it went to the recycler after that.