I say keep the Jetta, do that belt job/usual maintenance and if things start going south, sell it cheap to someone.
Best case scenario, you get a good few years out of it and save some cash for the next car.
Worst case scenario, you get couple of months and it grenades. 500 bucks lost. Life is a gamble anyway
I myself recently bought a 200€ passat. Maybe i got lucky, maybe i dont. At the moment it works fine.