I don't know what the Banks kit costs but of the components that we have installed for the Banks system probably only the exhaust headers, pipe and muffler are anything remotely unique.
The air intake could easily be built from off the shelf parts. The headers themselves are probably easy to come by from Summit or other race outlets. The length of the pipes and the muffler could also be easily duplicated. I would be happy to take pictures and provide dimensions for the pipes if you would like.
Whether the bang for the buck is there to justify the cost of the Banks system I don't know. On our Argosy motorhome where I'm doing the install of the new engine I will just buy parts from Summit, etc and build the system myself.
It seems you probably end up spending a lot of money to buy the two placards for the sides of the motorhome
just my $0.02