That is a clever design, and yes, it's doing the same thing. If you have electronics assembly skills, why not? Sounds like fun.

There's no reason a simple compressor suitable for your purpose should have to be expensive; there just isn't much of a market for such a device.

If you're open to used gear, another good option would be an Alesis Nanocompressor - available in the $70-$90 range: https://www.ebay.com/sch/i.html?_nkw=alesis+nanocompressor&_...