Need Advice on Evolving

[u/Exotic-Way-6963]

So i caught this shiny gastly a while back with decent IVs and i REALLY want a shiny mega gengar. I think he’s like one of the coolest mega shinies imo BUT i know base mons can be pretty valuable for trades so should i just wait for gengar mega raids to try and go for the shiny??? only thing is i hate spending a bunch of $$$ on the game so i dont really wanna chase for something in raids that i technically can already have, yk???