What? The monthly cost of a server is equivalent to a few hours of dev time. That's money better spent on making new things, not premature optimization.
I'm all for easy fixes that speed things up, but you rarely need to switch language/framework to do it. Doubly so because slower languages like Python and Ruby make it easy to plug in bits of fast C. More likely than not, someone has already done that, and you just need to start using a better library.