I charge what I think a job is worth.
I hate vehicle wraps - so we usually quote 2-4k depending on the job... Were quite a bit higher than the other shops around here, but if im going to do a wrap.... I'm going to make it worth my time.
My buddy owns a shop and charges $18-2000 for a full color wrap that takes a week. I don't know how he does it... He says he has to stay low or he loses to the shop down the street. Takes him 4 days to wrap a vehicle properly.
In those 4 days i can make 10x that selling
signs, for less work / less headache, and I'm not going to bed exhausted and aching from all the bending.
You don't always have to be the cheapest... But try to be the best. I wouldn't dig a hole for under $100, even if the going rate was $50... Doesn't mean it's worth my time to do it at that price.
Stick to what you know and want to do - price the shit jobs high, if you win it at least you're making decent Proffit, and if you lose it just look at it as your back isn't going to hurt for a week to make a few hundred bucks.