Cheap Solution for Streaming Audio Across Household

I'm building a system in the current weeks, but I'm having a hell of a time with one little solution...

This thing is going to be a powerhouse media PC, but it needs to send my PCs audio into other rooms in the house to be of any use.

It's harder than I imagined to find a well-reviewed solution to do this that does not interfere with a home wireless network - maybe even something that actually works with the existing Wi-Fi signal? I would certainly not mind if it was also able to stream video, too, but I'm looking specifically for the cheapest, workable sub-$100 setup, which unfortunately rules out Apple TV.

Any ideas?

Thanks for reading.