It's that waterproof fencing that gets ya!
When I was just feeding two Alpine milking does they would eat one 65 lb. (ish) bale of straight alfalfa hay every week.
They got Klassy goat feed both morning and night on the milkstand and I was buying a 50 lb. bag every two weeks. BUT, I also bought a 40 lb. bag of BOSS (black-oiled sunflower seeds) and mixed it into the feed. It actually took me several months to go through that one bag of BOSS.
They get free choice loose goat minerals, I bought a bag back in August and still haven't finished it yet (and I've added more goats).
I also give free choice baking soda which is negligible in cost.
I suggest having a CMT (mastitis test kit) on hand. I don't yet but paid my friend $5 to use hers once.)
I trim my goats feet myself (very easy to do), I already had the trimmer as I also use it on my llamas. It cost just under $20.
Shots and worming are a personal issue that you will have to research for your own area and talk to people and a vet around you.
You want good quality stainless steel milk buckets (at least IMO), a strainer (makes it sooo much easier) and glass jars to store your milk in.
I love the 1/2 gln. Mason jars but they can be hard to find except in the fall. A strip cup isn't necessary but nice to have. (Obviously these are a one time cost.) The filters for your strainer are on ongoing cost but very inexpensive.
I'm blanking out on other costs... certainly a good, draft free shelter is very important but can be very inexpensive to put together. Straw or other bedding will be needed.
I found wooden cable spools for free (took me a few months of looking here) so they have toys to get onto. I also got some free tires and buried them for climbing toys (although those are specifically for my NDs.)
The last things would also be a one time cost or effort so they don't count in your monthly expenses.
Edited:
Oh duh! A milkstand is critical IMO, milking a goat on the ground is hard on the back. Again, a one time cost - easy to make out of left over wood laying around.