Can you weld? Or do you know someone who can and will for free. This will save you a lot of money.
You will need slides
https://www.ebay.co.uk/itm/15-1500mm...oAAOSwyi9aJP-x
This is the cheapest I've found them and I have this exact set very happy with them, you will not find them cheaper than this new.
You will need a drive as well, ballscrew is your best choice here Ebay is your friend but expect £250 and maybe some import tax.
3. Variable frequency drive it's a inverter that drives the spindle. Spindles are not running 240v single phase they are 3 phase and need the VFD to drive them you cannot connect a spindle directly to either single phase of 3 phase otherwise you get the magic smoke. Water cooled spindle are much quieter if you need a water pump pay postage I'll send you one for free I have a box of them. £200 for spindle with VFD.
4. Everyone seems to go for 3nm Nema 23's ~£30 a motor, I have 2nm on my machine £20 a motor. You definitely don't want less than 2nm.
5. Breakout board to connect to parallel port on a PC, this means you need a desktop PC to drive the machine but it's the cheapest possible way (Yes even cheaper than arduino)
https://www.ebay.co.uk/itm/Mach3-CNC...AAAOSwhqhaRkJb
Buy 2
Think about how your going to control the machine you can buy Mach 3 £200 or use linuxcnc free I chose linuxcnc ;) You need to generate Gcode for the machine most of us are using fusion 360 for this but there's many ways of doing it depending on the job.
The best thing you can do first is learn! Read people diaries ask questions. If the job you have for it is profitable you can probably find someone on here to make them for you and still make money giving you a cnc fund ;)
But once you've done it you're in a special club for sadists that only members can ever understand lol.
It's also highly addictive ;) Most of us on this site would rather get 2 3m lengths of 25mm Hiwin's with carriages for Xmas than a new Iphone, which is the way it should be to ;
Now I built one I can say you build must start in cad! I thought I could build one without cad I was so wrong lol I was being idle. I could have worked it out on paper but damn it would have be sadistic and expensive with mistakes.