I've been in the same boat...not quite as bad because I've got a fairly large repeat customer base but they are not enough to keep me in business. I need new customers and the last couple months have been slow and the last 30 days have been almost dead for new customers. I've had the same results as you with much of my advertising except for the Yellow Pages, which are affordable in my area and have paid off in huge dividends.
I've been really struggling mentally with my business being so slow and to be honest, I've been praying about it and my business boomed today all from repeat customers. I picked up a whole weeks worth of jobs just today, including a HUGE job for new tractor dealership that will take over a month to complete. My point is, it's amazing how slow you can get and then BAM it all comes in at once. Granted, next week might be dead again....
I'm looking into direct mailings to local businesses. I was going to work on it this week but now I'm too busy. I am getting more and more business customers and they all seem to be less than happy with their current techs. I think, at least in my town, that is a huge market that can be tapped into. I've tried other avenues of ads like you and I'm thinking my last option for marketing might be direct mailings to business.
Oh one more thing to think about....I almost forgot.....I put some ads on Facebook and directed them to people only over the age of 21 in my area and I pay per click. I've gotten some decent business off these ads from time to time and the pay per click rate is CHEAP.