Future V8 owner
A cam is pretty inexpensive depending on what type you get, and installation shouldn't run you too much on that. If you are looking for a H/C setup, it will be the heads that cost the big $$$. Those will put you over that 400 mark you are looking for. The amount of power you make once again depends on what type of cam or cam/heads you use.
I personally would not recommend nitrous at this stage. Maybe a turbo system or blower.
Good idea to get in league with other V8 owners and specifically the guys and gals here on LS1Tech. There is more information on this site than in a whole stack of books.
Good luck, and never be ashamed to ask even the simplest question!

