If he wants to make +500rwhp NA. He will have big money in the NA build.
Very few stock bottom end cars have reached that mark NA. The lsx motors you see hit those numbers are ls3 and ls7 motors. Good luck finding either of those motors for less than $5K. Then you will need full boltons, ported heads, ported intake manifold, TB and a cam. You will have another $4-6K right there.
Yes, there are ls1 and ls2 motors that make 500rwhp but, you will spend $6K on the heads, cam, intake manifold and TB alone. Then you will have to buy RRs, electric water pump and all the other bolt ons to make it happen. I think I can count on one hand the stock bottom end ls1/ls2 cars that broke the 500rwhp mark NA.
You can make 400rwhp NA for your budget with the right parts all day long and a stock ls1 bottom end. Try to find an 01 or newer ls1 motor and go with an MS3 cam.