Can you convert a mini cooper into a mini cooper s? Like supercharge the mini cooper? How much would that cost?

 

Probably more than buying an MCS in the 1st place. There is talk of a bolt-on turbo for the Cooper in the works from a few companies. Do a search in the Performance Mods forum for turbo.
And welcome to MCO.

 

It'd probably end up costing you the 3k difference in price between the two, so you would be better of just buying one in the first place, but since you wana do this, I dont see why you wouldnt be able to.

 

The 3k difference is getting you a lot more than just a super charger. The internals of the motor are different. The S has a lower compression ratio to accomodate for the boost. You wouldn't want the compression ratio of the non-S with a super charger or turbo charger. Getrag transmission, heavier duty suspension.

If you are just going to just add a supercharger or turbocharger, you should figure in what you are not getting as additional cost. Said another way, take out all of the other differences between the two cars to correctly figure the cost of the super charger. It is not 3K for the super charger. It is probably more like 1k or 1.5k.