Joe, a couple of things here. First and foremost, if you give signs away for free, it tells people that the value of a sign is little or nothing, so in the future, you will have no pricing power with anyone you're giving free signs to. It also takes work away from someone else that does do signs for free. You run around town and give free signs to everyone and somewhere out there, there's someone trying to make a living making signs, who's now lost all his paying sign work.
You mentioned your overhead is low. What difference does that make? I'll tell you what it implies and what others are picking up in your words. It implies that you are going to do things really cheap because you don't have any overhead and you didn't pay much for your materials and equipment. The problem is that you should be charging what the market will pay, not what you want to charge because you have no overhead. If a sign has a perceived market value of $100 and you're charging people $35 for it, then you're destroying the market.
You are destroying it because you have no overhead. However, if you get flooded with work because of your low prices and you are forced to grow into a space outside of your home, you'll have to pay rent, utilities and wages just like others. So you're $35 for a $100 sign is going to put you in the poor house. If you call your now established clients that love your $35 signs and tell them that you need to raise the prices to $90 to cover your expenses, they'll drop you so fast it's not funny. Then, you'll have a new space, with a lease, and bills to pay, and no work.
You need to learn to price from day one. You price for the market, not for what you have in it. If I have a drop from a job that works for another sign, should I not charge the new client for the material for the sign?
Let's say the material is $200 for a 4'x8' sheet. That's $6.25 per sq. ft. cost. So the cost to the customer should be at least $12.50 per. sq.ft. Now, let's say I have a 4' x 4' drop left over from a job and it needs vinyl lettering. If the vinyl lettering price is $200, should I just charge them $200 and then give them the material because it was paid for from another job? Or should my price be $400, $200 for the vinyl and $200 for the substrate?
You don't give things away. You charge the market value. Not YOUR perceived value, but the MARKET perceived value.
If you don't get your pricing straight from the beginning, you won't have to worry about making $500 a month. The first time you get a job that has 3 colors in it and you don't have any of them (yes, believe it or not, people do actually want signs made from colors you don't have in stock), you'll have to buy 3 rolls of material. There goes your profit.
I'm not suggesting you not give it a whirl, but I would suggest you take another look at your approach. I think you're making some pretty large mistakes in your direction.
Just my 2 cents.