Used beacons are not a good idea. I know new ones are expensive, but that's the cost of entry to this game.
The best way to decide which beacon is for you, is to go into a reputable shop, ask them to hide a beacon, then give you all the ones they have for sale with no instructions. The one you can turn on and locate the hidden signal with fastest and most intuitively, is the one for you.
Members of Friends of Berthoud Pass
can get some great discounts on avy gear.
And remember, a beacon is worthless without education and good partners.