Only thing that you should be able to hold consistent is Hours charged for shop time. Not cost.

SC should have an expected amount of Hours to install, say 3 hours.

Then you pay 3 hours labor to install at your shops rate.
The cost of the Flow will vary but it shouldn't vary a lot because there is an MSRP to everything.

Just like buying a Boat, SC can tell you the MSRP of the boat, but the final cost of the boat is always up to the dealer selling the boat.

When we get ours installed I will share the Labor Hour charge, but the Shop charge and the price of the Flow will be different in my world then in yours I'm sure.