For 5k you should be able to find a decent horse. It might be young with little experience, especially if you are looking for a warmblood. But it is defiantly doable. Their are many other breeds that are good for dressage and can be less money. So here comes my next question. I see horses in my area for sale for around $5,000 (which would be near the max of my price range). Can I get a good all around horse with some dressage training for that price?
I am not 100% sure for your area but judging by the board cost shoes should cost around $170 for all 4. Unless the horse needs pads or something special.
Deworming can be done by the vet with shots for about $30, or you can do it yourself for around $5-$15 4 times a year, or you can feed a supplement for it which usually seems to cost more.
Teeth float is about every 2 years and would be about $200-$250. Spring shots are cheaper and usually around $20-$30 while fall shots are more expensive around $50.
Horse health insurance really varies by what you want covered and how much you insure your horse for. I would call around to get pricing it can be anywhere from $90-$500. You also usually have to pay a fee if you want to use it. For instance if you horse colics you might have to pay $250 but they will cover the surgery to $7k.