personally I wouldn't take a loan out...there are lots of good horses for sale in CA that would make a great dressage horse...if you don't have enough now, wait a year and save up...that's what I did...I saved up all my money so I could buy the horse that I really wanted.
THere is always a possibility that you won't be able to get what you paid for a horse or more if you try to resell them. Remember things can happen to the horse to decrease their value...lameness, scars (yes, sadly some people won't pay alot for a horse with alot or a big scar), hoof problems, etc.
It's a risk if you go about it that way
Will this be your first horse?
My suggestion is to get a less pricey horse to see if that's what you want to do...taking care of a horse is a huge responsibility that not everyone can do.
Buying a horse is a LONG term commitment...if you have to sell the horse in a year, why get it and have to sell it...not only will it be hard for you, but it will be hard for the horse.
If I was in your shoes, I'd buy a horse after you are finished with school, that way you have the time and money to take care of one for a long time