First of all, nice price on the Jetta!
Check the cables from the coil to the distributor and from there to the spark plugs first. Then take a look at the distributor cap and finger, the take out the spark plugs. Since you have them out anyway, you might as well replace them...
To check the coil, take a multimeter and measure the voltage between the two outer pins of the coil cable. It should read about 12V, take or give. Then take a LED light and connect one end to ground (minus pole on the battery) and the other one to the pin in the middle of the coil connector. Have someone start the engine. The LED should flash or flicker. If it doesn't, check the cable to the ECM. If it lights up, change the coil.