As a machinist, I agree, the mill is one of the best tools you can have as you advance in knife-making. I also agree with buying the BIGGEST machine you can afford. Small mills do not have the weight and rigidity needed in some procedures. Also, consider that most machines do not come with tooling i.e. a vise, cutting tools, clamps, etc.
Buy the best vise you can afford also, because a cheap vise will not hold up and they don't have the holding power. Price ranges for new vertical mills is anywhere from $4000 to $12000 approx. Again this does not include any tooling.
Lastley, you can buy an attachment to turn a vertical mill into a horizontal mill. I don't know how well they work, but they are not too expensive.
email your mailing address and I will send you some tooling and used machine catalogs that I have.
I hope I helped.