I may be a little biased, but…
Give MentalCore a try and see if it will suit your needs. A lot of work has been done to make this a suitable way of using Mentalray in a production environment. Its in beta now, so your can try it for free, and give me any ideas or suggestions that could help improve it for your production. We will be using it here at Oktobor Animation for some tv shows. It’ll be loads cheaper then investing in vray or prman. Its not going to instantly fix every single problem with mr, but it goes a long way to making the workflow easier - plus a much better render pass system 
