new guy here

[Bigdave196]

I'm the newbie, and I just bought my first BBC yesterday. I need a little help on a few things and a few answers so lets begin
I now own a 1991 Chevy2500, 4x 4, 454 with auto Trans, xtra cab, long bed that I picked up for $1300. It starts effortlessly, drives smoothly, shifts a little hard from first to second, and pulls like it should. I would like to get more power out of this motor and I'm going to add long tube headers, K& N air filter, and Full tune up. What can I expect from a cam , and how big can I go before I need to change out my valve train and what can I also to to improve performance before I do a total rebuild. what does an average build up cost to get about 400-500HP and are there any secrets to getting that on a budget.