To answer your questions in no particular order: The costs really depend upon a number of factors, with the hourly rate in machine shops around here going for about $60/hr (if only I got paid half that much). Some shops won’t touch “one-off” jobs, other shops can handle them with no problems. There are a number of different types of milling machines, some which use their own specialized language and others of which follow what’s generally industry standards, and certain machines can handle more complex jobs than others.
There are programs out there which will allow you to load an AutoCAD produced drawing in them and will then output the necessary machine code (generally as a .txt file) after you’ve input such things as machine type, material, and tooling. I do not know of any free Windows based programs which do this, however, and unless you’re willing to spend a couple grand on software, the Windows based stuff that’s relatively inexpensive is pretty kludgy to work with, from what I understand.
For what you’re wanting to do, here’s what I recommend: Check to see if there’s any trade schools in your area (or high schools/community colleges with a machine shop program) and give them a call. Odds are, they probably have a system for allowing the general public to get things machined for them at a relatively low-cost (where I went to school the fee was $15). You’ll probably have to supply the material, and don’t expect the job to be done quickly, but you’ll be able to talk with the instructor/student and find out what kind of equipment they’ve got and what the limitations of it are, without the meter running the whole time.
If you want to try your hand at generating the machine code and aren’t afraid of Linux, then check out the software offered here. If you’re feeling brave, you can check here for instructions on how to build your own CNC machine. Or, if you’d rather buy a homebased CNC machine, you can check out the magazines sold by these guys as various companies that build home sized CNC machines advertise in their pages and they also sell books on how to convert a standard mill to CNC. If none of those options appeal to you, you can post a request here, and see if anyone at that board (Yes, I do post there. Guess what my username is! ;)) can help you. If you’re not in a hurry, I can see if I can do it for you, or, if you can send me the CAD drawings in a format I can view them in (I don’t, at present, have the necessary software installed on my machines to view AutoCAD documents in their native format because it screws up my DVD-Burner for some reason.), I can take a look at them and give you some pointers.
Oh, and skip the exotic materials like titanium. That requires specialized tooling, which will cost you more than the titanium, and a lot of shops won’t touch it because it’s so hard to work with. If you’re looking for some kind of PC case components (google “WMD PC” for a truly jaw dropping case), I recommend going with aluminum. It’s cheap and easy to machine. Depending upon the alloy, stainless steel can either be no real problem to machine, or an absolute bitch to machine. I won’t even get into discussing machining things like monel or iconel as the applications for those things are pretty rare (not to mention the stuff ain’t cheap).
Feel free to drop me an email with any other questions you might have.