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If you find Overture and Google too expensive, then it might be you need to think outside the box on your product/service offering and pricing.
If it's low ticket items think how you can raise the average order value, for bulk orders maybe offer discounts, or free shipping.
Heard both positive and negative comments regarding Business.com for B2B businesses.
Thomas Regional has a new PPC program for industrial products...perhaps other directories in your market are doing the same thing.
I tried Sprinks 3 times and had really bad luck with it. They get click thru but I my clients never get any leads or sales.
Good luck.