I think .05 cents per request is too expensive. If generating a response is a computationally intensive task, then I understand. But your current pricing model reminds me of the pay-per-minute phone calls of yester-year.

Pricing has to make sense. Pulling from my experience building and marketing LinkPeek.com, I have found the best results by providing different tiers or plans for different target markets. I try to use the different tiers to show value for different types of customers. It should be a no-brainer for your customers which plan to choose.

I feel you should review your current pricing model so that you don't scare people off when they do the math.