It's going to vary from place to place. Personally, most of my horse expenses (board) are free because I work for the barn, but I have to pay for everything else. Here's the breakdown, including board:
Board: $500/month (includes hay and grain. Field board, no stall)
Farrier: $35 every 6 weeks (trim only)
Vaccinations: $75 2x/year (includes coggins)
Dentist: $90 1-2x/year (includes standing sedation)
Chriopractor: $200 as needed
Deworming: $2-15 every 2 months, depending on which tube I use
Now, in my area, this is CHEAPER than many. Why? We don't pay farm calls for the farrier, dentist, vet or chiropractor. There's 40+ horses on the farm, so someone always needs something. The farrier shows up once a week like clockwork, the chiropractor shows up every 2 months, the vet shows up every 6 months for routine things and about once a months she comes out and ends up seein 2-3 horses for non-routine things.
None of that includes tack, training, non-routine vet care, consumables and other supplies. If you're getting a horse, cost is the first thing you should be looking at. We can only tell you what WE pay under our circumstances. You need to do research to find out what YOU will have to pay.