I think the question of paid developer time is somewhat orthogonal to that of language choice, save for one element. In general you don't want to be the biggest user of a given language/framework/what-have/you (I'm just going to say framework to keep it general) unless you're willing to upstream patches to that framework and forego the advantages of broad use. Sometimes that's valuable if the framework is particularly interesting but in almost all cases you'll want a paid developer working on the project in a serious capacity.
However if the project depends on more common and robust frameworks then the issue of a paid developer is less of a problem. If we were choosing between coffeescript and JavaScript, it wouldn't really come up.
As for the language choice, I'd recommend JS but the project is large enough that rebuilding it in a different language may be too much.
-Adam