What is the cheapest CPU I can get to transcode four (4) 720p streams at once? Also how much RAM?

I’ve been running an FX-6300 for my Plex server but the power consumption sucks as I have been running it for 24 hours a day for about 3 years now. What is the least expensive CPU that can transcode four 720p streams at once and is energy effiencent?

Second question, how much RAM do I really need for a Plex server. I am currently using Windows but the new cheap, energy efficient build I am planning will be using Ubuntu.