First of all, welcome to the Forum! :)
Ally, are you taking lessons? That would be my first step, then leasing (or half-leasing) a horse to be sure you are ready for it. Co-owning a horse may cause all kinds of problems between the owners (unless its within a family, and even so).
Now I'm in MD (rather close to where you live, although I'm towards the cheaper county
), so here are the prices (approximately, of course, and they are higher as you go closer to DC):
Board will be from ~$250 (field, most probably no ring, usually not the best care) to $500 (with indoor and stalls). And it's better to look for the place where the horses are turned out most of the time or at least half of the day, not just several hours.
Farrier: ~$40 for the trim (shoeing will be $100+ front, $200 all 4), every 6 to 8 weeks. At the moment I go with 4 weeks in between, because they grow A LOT during hot season and unfortunately I can't do touch-ups myself right now. Usually it's 5-6 weeks Apr - Oct, and 8 weeks in winter for me.
Vet: farm calls seem to be around $60 for most vets I know although it depends on distance of course, and then you pay for shots and coggins (not sure about the price, just don't remember, but something like $150-200, all shots).
Floating: $80-100 (once/year)
Of course you'll need dewormers, fitted tack, brushes, etc. etc. etc.