What would a good entry milling machine cost to do things like this? Are there desktop models that would do well?
Depends on your budget level. I know people that have done it with mini-mills, it just takes 2-4x the length of time as using a more powerfull/better mill. IF you can locate a solid knee mill for shot money, that would be an option. Just know that you might have work to do on said [used] mill before it's actually good to be used.
I went with a new Grizzly G0761 mill (along with the stand) for all around milling work. I'm space limited, so getting a knee mill (at my current place) just wasn't in the cards. I've added DROs (from DRO Pro's) to the mill so that I have accurate positioning too.
Another of the reasons I went with the mill I did was how the speeds are controlled. I've had not so good experiences with variable speed machines (lathe) in the past. I didn't want to have to worry about a controller going wonky and F'ing up the speeds. With the six speeds selected by gears/levers, it's pretty much worry free. Most knee mills control their speeds via belts and pulleys. That's good until the belt starts to age and needs to be replaced. Or the tension isn't right and it starts slipping. Sure, it will take time, and all that. For me, changing the spindle speed is easy and fast (compared with the belt option).
Whatever you do, I would get a least a full horse power motor on the mill (even after a 3 phase to single phase conversion if you get a knee mill) so that you have enough power to do things up right. Also get something that uses R8 collets since they are pretty much the standard (easy to find items for).
Something else to keep in mind. You'll spend at least half of what you spend in the mill in tooling/accessories for it before you're done with the setup. Between a solid vise, end mill holders/collets, end mills, measuring tools, etc, it isn't cheap. I started off with a 4" vise (on a swivel base) but then upgraded to a 6" vise (no swivel base) and am much happier with that. Precision end mill holders also make things easier on you. IME, Shars has really good products for your machining needs. I bought the 6" vise, end mill holders and more than a few end mills from them. I'm eyeballing a rotary table setup from them as well (not sure if I'll get the 4" or 6" yet). I also like their digital calipers (have the 6" and 12" models now).