I have an 06 and love it. $20k is on the high end though. You should be able to find them for a few thousand less than that easily.
Here's some things to be aware of:
-flywheel is prone to failure. It's a two piece design with springs and grease between the halves to dampen power pulses from the engine. It's quite common for the flywheel to fail catastrophically and take out the trans in the process. Symptoms of a flywheel on it's way out are clutch slip, weird vibrations and finally a clutch pedal that stays on the floor. If it's under warranty you may be able to get it replaced. Best solution is to have a conventional flywheel put in yourself or at a competent mechanic's.
-camshaft tends to wear out prematurely. Usually this happens over 50k but might be earlier if poor oil was used. Some people have had no cam wear with over 250k miles and others have had to replace cams at 50k miles. Exact cause not really known. Best way to prolong the cam is to use a good non-VW recommended oil like Mobil 1 5W-40 Turbo Diesel Truck. Best way to check if the car has the beginnings of a worn cam is to pull the valve cover and have a look. No real symptoms until the valve followers collapse.
Those are really the two main things to look at. Overall these cars are very reliable and high build quality. If you have any more questions, ask away.
If you want more detail about the two issues I mentioned, check out the mkV section at tdiclub.com.