Tube Testers. Which to buy and where?

I'm hoping I can afford a tube tester, used. I'd love to be able to test output and input tubes, 6550, KT88, EL34, etc.
I've no idea how much they go for. I've looked on A-gon here, but I've no idea if these are worth pursuing or junk.
I'd even consider new if new could be had for a few hundred, or preferably much less. Then again, I'm thinking if they were that cheep, maybe everyone would want them?

Any input is appreciated.
Thanks,
David