I would say that a $200 price is a deterent that changes the value and size of a market, but it can't be prohibitive since many people continue to buy NFA items.
I do think that deterent is bad policy. Someone noted in this section not to long ago the prospect of suppressors being classified as AOW so they could be purchased with a $5 stamp. I would welcome this as a matter of hearing safety and courtesy to neighbors. Yet, a stamp that costs me as much as four tanks of gasoline (just for perspective) isn't necessarily the stuff of a constitutional violation.