Advertising?

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I've been thinking of using some of my earnings from PTC sites for advertising. I'm especially interested in ClixSense, but I can't figure out how much it costs to advertise. There is a form to fill out with how many views you want to buy, but it doesn't say anything about the cost, just sends you a bill after you submit the info. I'd like to know BEFORE I get a bill just how much it's going to cost. Have any of you used ClixSense to advertise, and can you help me out with how it works?