The machine I built for my business is an AVID Pro 60120 with an S30 ATC spindle. Even with the “plug and play” kit from CNC Depot, it was most definitely not plug and play. I have put somewhere between 30 and 40 hours into just creating, setting up and testing hardware and software related to getting ATC to work reliably in a carpentry environment. It was fun, I learned a lot and it cost a bunch. Since that machine is about making money and has since paid for itself, it is easy to justify the investment.
Like @DiscoJon says, I don’t think you will find any machine out there that matches the HDM in the same price class.
Stepcraft has an ATC machine for $5,800.00 but I see a couple key differences. First, it has a 1kw air cooled spindle rather than a 1.5kw or 2.2kw water cooled. You are limited to ER-11 which means 1/4" or 7mm (technically you can do 8mm but the collet is pretty thin and you have to be careful not to put the tool to far into the holder). It will also be much louder which may or may not matter to you. Second, and the biggest difference in my mind, I can tell just from pictures that it will not be nearly as rigid. The Y axis uprights, X axis and Z axis look weak when compared to the HDM.