If you're going that route, stick to names like ScubaPro.
Frankly, one of the best deals out there on eBAY is the Mk10/G200B or G250HP.
You can find those on eBAY, often with an octo and gauges, for under $200 from time to time - sometimes in essentially-brand-new condition.
That combination is one of the best-performers for warm-water (over 50F) diving EVER MADE.
Buying the same "quality" in a NEW reg would cost you upwards of $350, even from the mail-order discount houses like Leisurepro, and $500+ at any dive shop.
Yes, you'll need to have it serviced before you use it. But you'll need to do that for any reg you buy every year, so really, the only "hit" is on the first year's bill - figure $60-100 for that.
I like them because I can fix them MYSELF, so my "service" cost is zero, and they are the equal of the "top line" regs available today from Apeks and ScubaPro - but are a hell of a lot cheaper.
The Mk10 is also simple enough and has few enough parts that other than seats there is no part that is hard to get ahold of. Generic O-rings work fine for overhauls on it, and I can rebuild them in my sleep.
The Mk20 or 25 would SEEM like a better deal (as a newer design), but its not. It has the "newer" plastic-bushing design and thus is more of a pain in the butt to overhaul, which means that parts kits (which you will be buying since you're not the original owner) are pretty much required, as the annual list now includes a bunch of stuff you CAN'T get generically. The result is that the price of maintenance on those is higher - and you don't really get much, if any, better performance for the additional expense.
There is a LOT of crap on eBAY - buy solid name brands, and only if the computation of your bid, including an annual service, makes economic sense.