Maybe worth having a go on some smaller and easier parts yourself and at least that will cut down on the cost.
Seen it done and looked easy enough...although I don't think i would make a good job of it myself...no patience!
P13B6 BMW - Crankshaft Exhaust Camshaft Reference Angle Difference Outside Of Limit Value
Read more: https://www.engine-codes.com/search_codes.php?q=p13B6
Would check the timing belt / chain as if slack this could possibly cause this fault