I've seen workable projects for about $500
$2k-$3k for serious hobbiests
Okay. Maker Shop is not for everyone, but they have the big equipment. My son-in-law probably spent $900 for the time we were there. He's an inventor and needed to test designs. He designed custom electronics enclosures in CAD, then cut the steel on the CNC machine which used high-speed water jets. They have like a 10 foot square table. Place your thick metal slabs on grills atop the water tank, tell it where to start and it cuts all the nooks and holes and outlines of pieces. They rent by the hour of operation. If his designs worked after powder-coating and installing electronics, he would farm out the design to fabricators to do quantity builds.
Would be nice to have your own milling machine, but it is expensive (for store-bought).