With the right cam, AND expert assembly and tuning, you'd be looking at around 375-390 rwhp through an A4 with the $900 heads, and 400-430 with the AI $1800 heads.Here are probably your two best options if you're looking for power per dollar:
www.advancedinduction.com
and www.elliottsportworks.com
Anywhere between $900 and $1800, depending on how much you want.