You can go the "free" route with Kerkythea, which is TheaRender's predecessor. http://www.kerkythea.net/cms/
No GPU support or any real developer support in the last few years, but the "Boost" version is 64 bit. http://www.kerkythea.net/forum/viewtopic.php?f=3&t=10661
The interface is no frills and it does a nice MLT (Mutton Lettuce and Tomato), clay rendering and whatnot.