Well valtrex is generic now everywhere so it shouldn't be a money issue for most folks if they have decent prescription coverage with their insurance. Acyclovir is still way cheaper but if you have insurance coverage that makes generics low cost, valtrex is, as of this month, going to be WAY cheaper for you now :)
the technicality to the answer to your question is this - only valtrex has been studied for reduction in transmission to a partner.