I would estimate between $10,000 and $15,000. Probably more if you were paying for labour. Pretty serious investment in a 25 year old car that serves no other purpose. That's what it takes to be at the pointy end of the stick. Well that or a lesser build and some alien driving skills. That's also in what should be the cheapest ST class since the starting point can be a 25 year old Civic/CRX/Miata