I can tell you haven’t been around Audis lately.
A buddy of mine runs a foreign shop that does mostly German. Back in the day, like late 80s, I used to do quick rebuilds. I weld a little. Have painted some (short hobby class too, kinda fun). Sometimes I hobby wrench, but it's been a while. It's therapy for me if it's the right car.
Im no mechanic, but most of the engine stuff, brakes etc on an Audi are straight VW and available at Autozone.
Just to be sure, I checked and found the following random parts for a 2007 TT using Autozone's website:
Caliper is $52
Motor mount $83
Head gasket kit $82
Strut (Bilstein even) $89
Alternator $156
Those all seem pretty reasonable.
01 Boxster (your link)
Caliper $185
Motor mount na (keep seeing something that doesnt really look like a mount for $20)
head gasket na (Edit $120 from partsgeek.com)
Strut $263
Alternator $171
Boxster wasn't really that expensive either.