If your not going into the motor and you are only interested in a bolt on kit, then the K8 is limited to about 40-50 HP of power adder (~235 HP).
Ghetto Turbo kits start at about $3500, and for that low a boost you wouldn't need progressive wastegate controllers, etc.
Dry N20 kits start realistically at around $450, but you will probably end up spending another ~$500 on a progressive controller and a way to add the extra fuel (PC Hub, etc.)
Anything more than 40-50 HP requires going into the motor and doing work to the head, rods and pistons. Many will debate that you can go higher, but don't.
I run a small dry N20 shot every weekend at the racetrack and get about 10 passes on a 2 lb bottle (at $5 a pound), so the cost of N2O isn't too bad.