In the past I had people give me MAC suppressors for just paying the transfer tax, BUT that seems to have changed due to a resurgence in interest of the "Old School" big cans.
I sold a 9mm MAC 10 with a can, while I had it posted here for sale, several people offered to buy just the suppressor for $750.00 to $900.00. However, the offers came too late the can when with the gun.
Since I have seen other original cans go that high. A Powder Springs can would be the most valuable followed by RPB, then SWD. There are also MAC type suppressors that were built (and registered) from the parts RPB and SWD used to sell.