Before you go down the path of "easy to remove tanks" and regulators, ask yourself what type of shooting you intend...
...HAtsan aier tubes (at least the 180cc versions of the AT44) are resonably cheap. But becasue they continer the whole she-bang (air volume and valve) there is enough varation between valves that they don't shoot quite the same. Can be pretty close if you are lucky,or 100fps different if you are unlucky...
Or this one:https://www.gatewaytoairguns.org/GTA/index.php?board=12.0There are so many choices it's hard to choose.
There are some rifles that can shoot more than 100 shots on one fill.
Jsar Hawk and NightHawk Do but youll have to Wait till tomorrow!