I want to buy a precision and rigid milling machine to make small size aluminum boxes but for small or medium production. also I should use a CNC kit to have a CNC milling machine.
The backlash must be lower than 0.025mm or 0.001" and the accuracy should be 0.02mm. I'm thinking of buying a WABECO F1210HS ISO30 with Ballscrews but how rigid is the machine? I should spend $7000 for the WABECO F1210HS. Fortunately the spindle speed is 100 to 7500 RPM so it's good for roughing and finishing.

I have found another milling machine from Optimum company, OPTImill MH 25V, the price is $4000:

The spindle speed of the OPTImill MH 25V is 200 to 4000 RPM. As I use the end mills with a diameter smaller than 10mm (3mm to 6mm) so sometimes the speed should be higher than 4000RPM!

You see the cutting speed etc for the OPTImill MH 25V at page 32 and 33 of the below document:

Could you please suggest me a suitable milling machine?

I want to produce such instruments: