Since I kind of recommended the free WoSign CA in the past, I would like to point out the issues that have piled up. Mozilla has a writeup due to a removal discussion for NSS: (Yes I'm late with this post, about a month or two by now ...)

Since WoSign, or the person behind it, silently also bought StartCom we've now with StartSSL and WoSign two of the three free CAs in one hand with a questionable track record. That leaves everyone looking for a low budget option with Let's Encrypt.