Can someone estimate how much would it come to have all 1u caps of my 88 key KB replaced by clacks? 75 * x = ?

At a minimum you'd be looking at $30 retail * 75 = $2,250.

As a rough average, assuming you can get a fair percentage for under $100, plus the remainder for over $100, an average of $100 each would come to $7,500.

If you want rare ones all over, you'd be looking at $200 each, for a total of $15,000.

If you want one-offs, or really rare ones, expect around $400 each, for a total of $30,000.