Free Proxy vs Paid Proxy
There are quite a few providers of "free" proxies but highly anonymous proxies however are not so easy to find not to mention "free" comes as always with a downside, you either get served ads while using the free proxy or should you find a good highly anonymous proxy for free, it will not be reliable due to high traffic loads. There is also the risk that the highly anonymous "free" proxy is actually set up by a hacker looking to get your private info like credit card number.
On the other side, paid proxies are actually cheap at 3-5 USD/month per proxy and they are always available for you 24/7 at high speed connections. Considering that you have 24/7 support on paid proxies and a guarantee for less than 0.01% downtime paid proxies will turn out to be a better option on the long run.