I would guess around 12k

An s2000 is a really nice car, yet car payments suck.

If you keep the gsr, sell the greddy kit & un-needed hondata.

Buy:
JG intake manifold
Full-race turbo kit with a gt30 a/c & p/s compat (for a stock b18c1)

If you really want to go fast, get some pistons/rods maybe sleeves

Good luck with your choice.