This is actually contradictory. Cheap and high quality barely exists. IN what niche do you work. Adult is relatively cheap and some offer "quality" traffic.
I've yet to see any pop up traffic convert to anything, cheap or expensive. In my experience, adwords seem to really provide converting traffic, at a high price though.
seoclerks seem not working for me really. but there are tons of adnetworks depending on the niche you are into.
I wouldn't go looking around for 'cheap traffic' that's one of the worse things that you can do. I mean if you buy something that is cheap, then you're going to get what it's worth, and in the end it won't be good for you. Honestly, if you want to make sure that you're site will be good and get traffic spend a little more so that you can get GOOD traffic, and people will come to your page.