How Much Does the Alloderm Grafts Cost for Reconstruction?

Short answer -- $41,580 is probably the amount the hospital bills insurance for a 16x20cm piece of dermal matrix, but your insurance pays them substantially less than that. You should not be billed for it, but rather your insurance. 
Long answer -- The hospital pays about $10,000 for these large sheets, but possibly less depending on what priced they have negotiated. I know more about the smaller sheets and facilities I worked at payed $3000 vs $5000 for the same thing. The hospital then essentially, as far as I can tell, "makes up" a price that they bill insurance. The insurance has a limit on what they'll actually pay and the hospital has to accept that assuming they are "in network." A crazy example about costs in healthcare is an EKG (heart electrocardiogram). If you look up costs, you will see anything from $50 to $3000. It is a simple test with stickers and wires and a relatively inexpensive machine ($400 on ebay) that an experienced doctor "reads" or interprets in a matter of seconds or minutes at most. 

I cannot comment on the charges from the hospital for Alloderm, but while it is expensive that number seems to be an order of magnitude too high (at least based on list prices from the manufacturer.) However, there is always a markup from the hospital. That question aside, I will say that Alloderm has transformed how breast reconstruction is done and has made a huge difference. There is little doubt in my mind that it has improved results and the patient experience.

The big sheet 8x16 sheet costs around 5-6K. Since you have only one dimension "16X" I'm not sure exactly how big yours was, but I can't imagine your surgeon needing a bigger sheet than that. Remember that the hospital bills for everything, and you are probably looking at your bill from them meant for your insurance company, not a bill to you. Wait for your final bill and your EOB to determine your real amount due. Good luck navigating the system, it is a nightmare.