The costs depend on 3 main factors:
- Where you are. Professional stables cost about $200 per month in some areas, but 3 times that in others.
- How you keep the horse. Starting from highest to lowest: professional stable, self-stable, field.
- What you use the horse for. The more you ride, show or compete, the more costs there will be.

For an explanation of all the costs and an online calculator, check out Horse Cost Calculator.

I would suggest you approach it this way.....

First calculate one-off costs. These include horse, saddle, tack, rugs, riding clothes.

Then calculate the cost of keeping the horse. Stall, food, bedding, insurance ($40/month), farrier ($30 6 times a year, double if you need shoes), annual inoculations ($100), annual dental ($100), mineral/salt/insect sprays/assorted (allow total $40/month).

Then add on costs depending on what you are using the horse for. Riding lessons, shows and exhibitions all cost. Look at all the costs associated with these, including transport, wear on saddle/tack/clothing, overnight stabling.

Then add 25% for things you didn't think of.

Reference vet bills, they can range from almost nothing to thousands, depending on luck, insurance and how quickly you spot injury/illness.