I find it hard to believe it's that hard and expensive to replace.
HOWEVER, I'm not familiar with those so if it is that bad perhaps an in-hose thermostat assembly from a '98 Sable would work. Yes, I was surprised to find out on that car that the thermostat lives
underneath the engine, in it's own little housing. Never saw anything like that before.
It wouldn't be a good thing to have to continually wonder if the "fix" is going to need fixing.
How to Replace the Thermostat in an Audi A4 | eHow.com
Google
It doesn't sound that bad a job, and no more expensive than any other vehicle. I'd fix it with the "right stuff" in the "right way". Actually it looks like gathering up the "redneck" parts required would cost more than the real stuff.