I have been advertising my sites through http://adfarm.org . It is text links cpm based, but the minimum is only 5 or 10 dollars i believe. I buy an ad every couple of days and this has been working for me. You get to choose what site you want your ad on, and there are different rates for different sites. I have been getting good quality targeted traffic from this program. Great people who run this program, too. They accept paypal also.
Oh yeah, and most importantly, these other ad companies need to learn to accept paypal when they adopt these smaller rates .