Honestly, I build Custom enclosures, My Starting price for them is 150 price goes up under certain circumstances.
Amp wire kits with RCA, Rem. Pwr/Grnd in 4 ga. is 85 for installation

The "gernaric" Dynamat your speaking of may very well be Extream and if so its way better thasn the crap you have to heat, thier is a tenique to installing it, but you could do it yourself.
Dynamat installation is by the hour, my rate here is 40/hour so it all depends upon how much your looking to install.

Wiring the subs and installing them into an enclosure is usually 20/sub because of impeadance (2ohm etc...) and amp tuneing is usually 50/1st hour 35 each after, but usually takes less than 1 hour

Fabric to cover the enclosure is up to the customer and could range from
25 bucks and up

anything special adds to price, and I am a little confused as to why you'd bother useing birch?
What subs are they and what are your plans?
If you do not plan to compete and your running Name brand subs like Kicker/JL/Rockford then you'd be best off using MDF, UNLESS you plan on removeing the enclosure frequently

So in my eyes 800 is too much, but 500+ is reasonable. IMO