The GoodWill Stores here have caught onto the interest in thread injectors, the prices recently have gone from $19.00 up to 40 or 50, without any extras like feet. 99% are junk.
Salvation Army has some good deals, I found a very nice machine for $12.00, with all the attachments, it runs very well, I would have paid that for the Walking Foot alone. The darned machine weighs a tone, not much plastic in it. I see a lot of men at yard sales looking over thread injectors.
You really need to know what you are looking for, the machines are out there, but you need to know what you are looking at.
Very much buyer beware, I would also be very cautious where there have been floods within the past year or so. You probably do not want a machine that has been wet.