A little late in the mix.

Total cost.
Depends how far you want to go. The type\brand\quality of ball screws can be a big factor. Then there's open loop steppers vs closed loop steppers vs servo.
After that is the control infrastructure, Mach, grbl, Linuxcnc or other. Then with Mach & Linuxcnc there is a choice of using Parallel Port hardware or external motion control. For Linuxcnc the most popular and well support external motion control is the Mesa FPGA cards, with them you have the choice of PCI, PCIe, Ethernet or SPI in the case of the Raspberry Pi. Tho there are a few projects that are repurposing the NVEM boards with custom software, another that repurposing ColorLight FPGA boards. Or there you can use a Orange Pi with the H3\H5 Cpu that uses the on die mcu.
Then after all that, there are PSUs and control boxes to think of, and of course wiring, switch, pendants, lights and a thousand other gubbins to think of. Then theres the chance you may need to buy quality crimpers, after a while you get sick of the cheaper stuff.

Now after all that here comes the expensive part. What vice are you going for, are you going to use standard collets or if you have an R8 spindle the Tormach system or the cheaper chinese knock offs.

Then after a while you are going to want a coolant system and then after dealing with the mess an enclosure\tray might be next.

After that point you kind of put the total cost to the back of your mind as you don't want to think about it.

And finally depending on the country you live in postage\delivery\taxes can add a fair amount.

Unless you're buying an actual factory cnc mill it's hard to put a price on it.

And here's something.......after a while you realise that some of the tasks you do were quicker when the mill was manual.

And the final kicker, the mill you have will be a little bit smaller for the task at hand.