it really does depend on the horse, and whether you are keeping them at home,or at livery!
I keep my horses at home...so no outgoing payment there.
they have 2 rugs each - mine are about £50 a piece, so thats £200....but thats a one off payment until they ruin/grow out of them...
My tack was cheap as I found somewhere that was changing stock - say £200 - that'll need changing at some point though...and prices can get VERY EXPENSIVE.....having said that, some horses come with tack and rugs when you buy them....and they probably wont need replacing if the horse is full grown/or has treeless saddle, and doesnt rip its rugs.
the local livery yard here is £90/wk, per horse and £70/week per horse...so not cheap. But the former does have an indoor sandschool with jumps, a horse walker etc....but they dont come down on price, even if you only have horse at grass, and dont use other facilities.
My horses arent shod, so thats £30 every 8 weeks (for both horses to be trimmed).
My horses get no extra feed in summer - so i save some money there...
They get hay 1 bayle of hay between them everyday from Oct/Nov-Feb/March, at £3 per bayle.
Both of my horses are still growing, and winter grass is rubbish here, so they get a little extra hard feed when its really cold - say £100 tops for the winter months...(but when we were in Cornwall, we had good grass all year, so I didnt really feed anything other than hay in the winter.)
vets fees are expensive...I use the Northern Racing College's vets...so they are quite expensive...but I have a good first aid kit, and have a fair understanding of the horses anatomy, so only call the vet out if a horse needs stitches/is REALLY sick. Otherwise, I generally have my own antibiotics (I call vet before administering though, just to check...but it keeps down call out fees), and I buy wormers online in bulk - say £100 a year MAXIMUM for all horses....
hhhm....older horses need their teeth checking 2x every year, not sure how much that is....Ive always had youngsters, and only had dentist out 1x to do them all...and cant remember the cost...
Smaller native ponies, and cobby type horses will generally be the cheapest to keep as long as their health is good because they keep condition well, even in fairly poor grass, they are hardier - so dont shiver off all their condition in the winter, keeping feed costs lower, and they are more sure-footed, so dont injure themselves as much as, and their skin/hair is usually tougher/thicker, so they stay warmer in the winter, and dont snag their skin as easily. Having said all that, there are always exceptions to the rule!
all in all, keeping a horse can get quite expensive at the best of times!