BMW Cylinder Heads

Can anybody tell me an approx costing as I have no knowledge abourt cars. I have a BMW 750Il 1990 which was leaking water. I was told it needed the heads taken off... Apparently they were redone at a machine shop and then when they put the car back together they BOTH failed. I purchased 2 replacement cylinder heads. This has taken the garage approx 11 months and unfortunately this was a barter. My original estimates were between $2400 and max $4000 from other people. The garage also broke the plate by the egine behind the fan belts when they were taking it apart.

Any comments would be welcome
Thanks

Im gona take a guess but 1-4 grand at a dealer. I dont know the exact price but a new engine in a 3 series costs 7 grand.