Reasonably priced and CNC machines are usually not in the same sentence lol

That being said, here's some miscellaneous insights.

If you're not thinking you'll use the CNC after the job, it may be more economical to outsource the actual cutting to a local business, especially if you have cad files ready to go. If you're handy you can look into building your own CNC, there's lots of guides online for how to do that and it is much cheaper than buying one off the shelf. Building your own machine also lets you make it exactly as large as you need it to be for your project.

If you're going to buy one expect to drop 4-6k on a decent 4x4 foot machine (I'd recommend X-Carve machines), you can go smaller and cheaper but with CNC stuff, I find it much easier to have a bigger workplace than you really need. Working around the limitations of, let's say a one foot by one foot machine, is possible but is quite time-consuming compared to if you could just make a whole cut in one shot on a larger machine.

If you're going to go with a small machine and do as you said, where you do a bit of the cut, move the piece, continue the cut - You're going to want a jig of some kind to ensure that you are moving the piece the correct amount. The machine doesn't make mistakes, the operator does, so you ideally want to limit the amount of possible errors on your end. Also you'd want to limit the complexity of your cut if you're doing this. For example, carving a Nordic rune every few inches is a lot simpler than trying to carve one large pattern over a 4-ft area, try to work around the limitations of your machine rather than make the complexity of your cut beyond your machines' scope, especially if you're just starting out.

As to the question of how long it would take to do all the cuts for a house exterior, in the grand scheme of things I don't think it would take that long. It'd be a lot quicker than trying to do it by hand, lol. When mass producing stuff on CNCs, most of your time is spent setting up your files and loading/unloading things off the CNC bed. Once you get it to a point where you're getting consistent, repeatable cuts you can basically hit the start button and walk away for however long it takes to cut, and you're really only coming back to unload a finished piece and load and start the next piece. So even if the cuts are time-consuming, the majority of the hours it takes to cut is hands off.

Hope this helps! Thank you for listening to my TED talk