I did spend $5600 on my horses surgery last year. So yes vet bills can get expensive. But, not every year.
Before that surgery, I spent probably nothing on vet bills. I have never had a major bloody incident that I couldn't take care of myself, but it could happen. It helps when you know how to vaccinate them yourself.
Still haven't needed to have my own horses teeth floated and he's 10 now.
As for tack, if you keep it in good condition you won't spend much on it from what you initially pay.
We train our own horses, and I trained mine.

My horses are in my backyard, boarding is the cost of hay which is anywhere from $12-$20 a bail.
They are a lot of fun, but expenses are unpredictable sometimes. If you want to cut down on costs it's best to learn how to do things yourself.