I’m assuming you mean changing the roof. That part is easy & Jason at Next Level can knock it out. You can touch up the paint and be on your way with a new look.
For a real “conversion” it’s going to get expensive fast. You are going to tear down the car. Change the roof line, update components like shocks, hubs, steering rack the price starts to climb. A full sheet metal body can run $25k. Sand blast and re-powder coat $5000. Re-wire the car $5000, re-plumb the car $3500, seats? Interior? Windshield?
It gets expensive really really fast. The re-do I’m selling for $140k cost me over $180k including the car purchase. Granted everything on my car is brand new.
Based on my experience I wouldn’t do it again