mfarhan , do you need 3 axis motion control or just z will be fine ?
If trying to make your own - you have to find precision spindle or make your own. If you try to make your own you have to look for precision bearing for spindle. I dont know whether you can use something like dremel, i think their spindle bearing are not good for 100 micron hole making.
Anyway you can study drill bit manufacturer documentation for spindle requirements .
Z axis control can be done using ball screw with stepper or servo motors. PC control soft such as MACH3 or turbocnc or EMC2 (the last is free and rest are low priced) can supply control your axis through parallel port.
For pricing just for z axis (usd):
let say made in Chine stepper - 30 - 40 ,
controller (good one) 100 -150 ,
ballscrew (may be zero backlash ) with support bearings and motor coupler - > 300 ,
mechanical job (that is country dependent),
linear bearing fo z -axis - 30-50
spindle precision bearing - ?
high speed spindle motor - ?
Check cnczone.com site for more info . There you can find links to even cheaper premade alternatives in ebay . I guess the toughest (most expensive) point is spindle .