To anyone reading this, please don't do this to yourself.
A7 II is old MILC with a lot of quirks of early MILCs and generally not really nice camera to use. RP on the other hand has worse dynamic range than APS-C cameras (compare it to let's say Fuji X-T20 and Fuji wins by around half of stop anywhere between base ISO and 1600).
Z5 is only decent camera in the comparision. If you really want to push full frame, used Z6 and maybe A7 III (depending on deal) can be recommended. I would however personally go for APS-C as FF will also have more expensive lenses and if you push budget, FF is not the way to go.
As for APS-C, there are Sony and Fuji with mounts full of own lenses and third parties. Sony has cheaper (and usually bit less premium) first party lenses, while Fuji first party lenses can push into FF territory with price. For budget focus on Sigma, Tamron and Viltrox lenses. Canon and Nikon can't really be recommended for APS-C options, unless you have older adaptable EF/F glass.