V8 best bang for buck?
 

I currently own a 1996 automatic 300zx N/A with a locked up engine :( decided to get a daily driver and turn my Z into project car. I’ve heard people say I should just put a ls1 in it but I also know it takes a lot of fab work to fit in it and I’m also wanting to eventually turbo it.. I’ve read some more about a q45 and other V6 and 4 banger engines, my question is what would be the best engine for performance increase and isn’t too expensive to work on? I’m not sure my budget yet but I’m looking into getting 500-600 horse power. Ps, it’s automatic and I’m not sure if I want to swap it to manual or not...