If I understand correctly, you want to use this machine for milling steel and aluminum, and you have a budget of a few thousand USD.
Just buy a used milling machine. Preferably a CNC, that way the hard work is already done. Then upgrade as needed. No point in reinventing the wheel.
For instance, I paid $1000 for my 32x12.5x12 (10x52 table) CNC machine that was in nearly perfect mechanical condition. I did a controls upgrade later. A friend of mine picked up a similar, but heavier and with a tool changer, machine for $2500, and we did an upgrade on it also.