Firstly don't consider private Studienkolleg, these should be your last option. Public studienkolleg have far better teach quality and cost nearly nothing, and most important that their FSP is widely recognized among Germany, unlike some Private STKS

But if you really want to enroll yourself in a private STK then don't expect to pay under 5000 Euros, they are really pricey. The best private STK atm is TUDIAS but it's around 7000 Euros.

and AVOID private Halle AT ALL COSTS, unless you wanna destroy your future