I like the RWS 48 in being a sidecocker but I am leaning towards a gas piston instead of spring piston.
What would be a good option to the RWS 48 gas piston wise that is not a break action barrel type?
I want it is 22 cal, used mainly for pest control and plinking. I looked at the 350 gas pistons but they are a barrel cocking unit.
Prefer to keep it at around $400

As a side note what is going on for the demand of air rifles during the china virus ? (No Chinese air rifles need to apply)

I’m 46 and have a 177 M48 I have had since I was 14 or so. Been factory rebuilt once. Great rifle. You get pretty quick at cocking and loading. Has some recoil and the only real problem I ever had was the front sight sliding from it. Loctite solves that. There are some upgrades to the piston and spring you can get that will smooth it up even more. Never messed with the other type, but it would have to be a huge difference in performance to make me want to switch.

Both kinds of spring (gas ram is a spring) are about equally reliable.  They each have their own quirks, but for the most part there is no distinct advantage of one system or the other.  Steel springs are a bit easier to get replacements when they eventually break.  Likewise, the gas rams will also eventually fail.  Some of the gas rams can be charged to different pressures, which allow for easier tuning.  Steel springs can be shortened, to lower their power.  New springs are needed if you want to go back up, however.  Don't let the fact that the springs will eventually fail, for that usually takes more than 20,000 shots (providing you never dry fire it).  

There is at least one "drop-in" gas ram that fits the RWS 48, but as I recall, it is not an adjustable one.  The pressures of the gas rams, is also rather high and takes a small volume pump to charge them, for the larger pumps used to fill PCPs are difficult to get the required accurate pressures.

The only slight advantage that the steel spring may have over the gas ram, is if you shoot at widely varying temperatures.  The morning freezing temps will have a different power than the afternoon mid 80 degree F with the gas ram. The steel spring does not suffer from this effect.

I had a .22 RWS that I put a LOT of tins thru it. I know have an Airarms Tx.
Springers are hard to beat for performance and ease of tune up and the cost when required.