OP, understand you will probably spend the money and not get it back, that is part of the learning curve. But maybe you will do good from the start.
I agree with Shanna_Doll the best way to go about this in the beginning (cheapest route) is to contact website owners directly and get ad space that way. I personally do not have time to do this so I was thinking of hiring a VA to do this for me.
Sitescout is iffy to start with because they have some high traffic sites that will burn through your $1k faster than you would think. I haven't tried POF. I am also on BuySellAds, they may be cheaper in the short run but I have seen people complaining about the traffic they got - specifically it did not seem legit so be careful and understand how many displays you should be running for your spend.
Cheers~