Heck, I'd be inclined to just grab a Leshiy Classic. Easiest barrel swaps there are, and tuning is also very easy. You can carry a buddy-bottle and be fine for many many many shots. It also is superlative shooting freehand. I only bagged mine when swapping scopes.
Otherwise- and I know this may contradict some of what people are looking for- my 2nd Gen Fortitude is my premiere pesting gun. I leave it at the factory tune, get lots of shots, and it is dirt cheap.
Otherwise, I'd lean in the direction of an RTI Priest or Prophet. I have done commercial pesting specializing in avian abatement, and at the time, we used an R-7 and a Blue Streak pumper- yeah, both in .20. I wish I had a PCP back then.