Wow, could there be a question with a broader range in answer than this? LOL
My horses have never really cost a fortune and hey were/are all WELL taken care of.
My current costs for a 2 1/2 year old colt.
Shots per year, about $250.00
Farrier does all four feet for $45.00 every 2 to 3 months.
Doesn't need teeth done so far.
Paid maybe $50.00 to $75.00 for grooming supplies that I've taken care of and hadn't had to replace much yet. Brushes, hoof pick, curry comb, etc. Fly mask, spay, shampoo, etc.
Good grass hay is about $7.50 a bale here, so for hay anywhere from $700.00 to $1,000.00 + a year for hay.
He lives at my house so no board cost, and he pretty much accident free so far so vet bills have been average.
Oh and wormer about $20.00 every few weeks.
It costs as much as you want it to. Horse health and safety is first, so if that can't be done, you can't afford a horse. If you can and have room to spare for emergencies, changing economy and all the little goodies your baby just has to have(guilty) it should be smooth sailing. (: Lol
P.S. God bless your Dad for his service and I hope he comes home to ride with you soon!