Don’t underestimate your stock reverbs! The plugins DAWs come with are seriously underrated.
I have a lot of premium reverbs, but I still use at least one stock reverb on every one of my mixes. They sound great, and they’re usually pretty light on CPU.
Expensive reverb plugins won’t help you if you don’t know how to use them. Getting really comfortable with your stock reverb(s) will make you a way better mixer.
Before you go out and buy a premium reverb plugin, spend some time with the one(s) that came with your DAW.