I have to disagree with this Lauren. Good doers & natives aren't necessarily cheaper, often their needs are different rather than less. For instance a very good doer may sound cheap because it can live on fresh air BUT you might find it very hard to find a yard that can cater for that and end up with it muzzled (if you can keep it on) or stabled all year round and having to exercise it every day to avoid major (and expensive) health problems. They don't necessarily have good enough feet to go barefoot, particularly if you have to work them harder to keep them healthy & how often shoes are needed depends on foot growth. I'd say the main costs are often similar, things like hard feed are relatively small part of costs unless you're keeping at home, not having lessons etc etc. Buying something because you think it can be kept cheaply is a recipe for disaster imo.
Completely agree with you carthorse, swings and roundabouts I'm afraid, not all TB's cost a fortune (mine didn't) and not all good doers are cheap or necessarily easy to keep.