I put a search into Beeman's site for gas piston and got no results. I think those are going to be co2. ADD: I have not shopped air guns in a little over twenty years. there may be something else out there. For simplicity and operating cost, spring piston is the way to go, IMHO.
There are many makes and models to choose from. I never considered hunting when I choose mine. I picked a target grade break barrel, walnut stock model 55MM from Weihraugh. It is not high velocity, and it fits my needs perfectly. I shoot in the garage using a cardboard box with vertical stacked magazines as a bullet trap. Something over 550 fps is advertised. Ten shot groups of one ragged hole .25" outside to outside are expected (from a bench) with either the excellent aperture sight system or with a scope. Velocities twice that of the 55MM are available. Prices run from sub $100 to several hundred, depending on quality.
Side lever cocking models are also available, but the good ones get more speedy. The sky is the limit on those.
A tip: If you scope it get an air gun compatible scope. I trashed a regular Simmons with shot #2. The spring recoil is just the opposite from that of a firearm? A Burris Mini-4 PA and a Leupold Ultralight 3-9 EFR have both served me well. (You will need an extra scope stop or two, on the rail to keep the scope in place. it looks like a base without the ring.). Neither is marketed as air gun, but they stay together. You need close parallax adjustment for accuracy. I shoot at 33'/10m.