A good 'hint' about tuners is to figure their power handling is given in 'Pep', not average power. So it's rating should be 1.5 to 2 (or more) times whatever you anticipate putting through it. It's a matter of being able to handle the voltages present with impedance transformations. That typically means big capacitors with wide plate spacing, and that typically means that the tuner's 'box' is going to be large. Some things you just can't miniaturize, you know?
The used market is a possibility, but like anything 'used' you wanna 'raise the hood' to see what's in there. Lots of 'possibilities' there, all of them are not good. Brands? MFJ, Ameritron, B&W (B&K??), Murche, Heath Kit, and I don't remember what else (late night, not enough coffee yet).
Have fun.
- 'Doc
(How big'a tuner do you need? That depends on it's power handling ability AND how far 'off' the antenna is. If the antenna is 'off' by quite a bit, nothing is going to make it 'better'.)