The cost for parts to do a HG replace is around $125 if you buy from AZ Autohaus. Of course you may need additional work done to the head if it is warped. And if it's cracked, forget about that head. You will need special tools to re-assemble it correctly, though. Not sure how handy you are with a wrench, but if you are considering doing a swap, you should be.
This is what I would do... Remove the head, and take it to a mchine shop and have them work it. If it is cracked, they'll tell you. And if it does not clean up within spec height, they'll tell you that, too.
By the way, you can have it machined under the bmw spec if you buy a thicker than normal head gasket. Cometic has some options on that but they are pricey at about $170.
Bottom line is that is is relatively cheap to find out what the problem is by doing some disassembly and inspection. Then you can see how much it costs to fix and if it's worth it to you.
Good luck |