Scarry to have 1 gallon of loose gasoline under the car. Bad things happen if the fumes are comubustible.
Never had the problem but I'd suggest you get the car to a very competent mechanic/dealer ASAP to have the fuel tank pulled. Not something that a DIY person should be goofing around with. Just my opinion.
Regarding the $500. price, you probably go a very good deal. I have 137,000 mi. on my '93 TSI. Runs just fine. Recently went Seattle to Portland and return. No problems. Onboard computer kept saving that I was getting average of 29 mpg. at 70+ mph w/3 people in the car and no luggage. 169 miles each way.
If you need parts, do a little surfing at "www.car-parts.com" which is a search engine for junk yards. Easy way to find repair parts.