What's the ball park figure?
How long is a piece of string?
As for; "do you need a mill?" With out a doubt!!!!
I bought a Hafco HM50 Mill/drill and although I do not use it as much as I would have hoped to, would be lost without it.
Recently had some very close friends visit on their BMW bike, as they traveled around Aust. The bracket holding their coms unit broke and while the girls went out to sip larte, us two boys went out to the shed to play with the mill. We only slotted a few holes in some ally angle for a new bracket and then for the hell of it, sliced an old ally scuba cylinder in half with a 30 degree bevel, milled off a flat spot for a hinge and made a mail box out of it. Me old mate had never seen one before and was so impressed, as soon as they arrived home, began the search for one.
I will add the worst part of my mill, is not being able to afford all the tooling. You always want/need more, and it is so expensive (good stuff anyway). Mine is INT30 (or) MT30 taper)) and I believe the R8 size taper stuff, is considerably cheaper to purchase.
When considering the purchase of a mill, it is a good idea to also think about the basic tools you will also need to get the most from it.
Collet chuck & collets, drill chuck
End mills/Slot Drills,Boring bars/boring head, Face mill
Clamp set, Parallel set, V blocks, Vise (possibly a rotary as well (with indexing)) etc
Dial indicator (& magnetic base), Digital Vernier caliper (minimum) Micrometers (better), Edge finder, etc
The list could go on, but I would say they are the basics.
Ed