Go to the local art supply shop and get yourself some hard chalk pastels (they come in a **** load of colours). Grind a little up, add some water with a copious amount of dishwashing liquid in it and presto, instant panel line wash that is cheap as chips. The thinner the mix, the more translucent it is, so it won't give you harsh black panel lines (unless you want this)
Slap some on the panel lines let it dry and wipe off with a damp lint free cloth in the direction of the airflow. Do this over a gloss coat so it won't stain the paint. Best of all, it's much cheaper than MIG or any of those 'specialised' model pigments.