Have you looked at the FREE Kerkythea renderer?

Have a look at Strata in the way of a comparrison chart of what it does compared to  the Carrara version.
Analyse the Strata costs for the extras/plugins etc. Then also, compare how easy it is to use and what story you can get from forums on it's tendency to crash etc.
How good is it to use/understand from the trial version?

bwtr