Low price and quality that's never should be in same sentence Adwords Facebook Ads This is the 2 i would buy traffic from if ever i will have money to spend in such way ...
I hear that you get alot of traffic from the Link Exchange Providers but I asked the guy that working my blogs and he told me that some link exchange providers can be harmful to your ranking and than helpful. He also told to keep submitting my articles the different directories.
Aside from Adwords and Facebook ads, I don't think there is any point in buying traffic from some sites that offer so. Traffic with no possibility of conversion is as good as nothing.
Google Adwords, thats your best bet. Although it would be good to look for organic sources of traffic. Have a read here - increase website traffic.
My traffic is real if you need some, I tried it myself for my websites so I can guarantee the quality.