[mootothemax]

Do you cold call them about an online product/webapp?

Absolutely - at the very least, send an email, but phone calls are always way more intimate, as long as the person you're speaking to is receptive to the idea of speaking to you in the first place.

Adwords is too expensive when you are not sure if there is demand for the product.

I'm about to experiment with this. Honestly, if I could spend $30-$50 to validate an idea with real, live, targeted visitors, I'd consider it money well spent. The only lingering thought I have is: is that too little to spent?