Very difficult to quantify without knowing what type of horse/pony you are looking for. Feed wise a TB type would require a totally different ration to say a native type. Ball park on shoes say around £60 per 6 weeks then you will have your worming, regular vaccinations etc etc. If you are stabling, then bedding will have to come into it as well, this varies in price with straw usually being the cheapest option. Hay is also another regular purchase you will have to make.