I wouldn't disclose the amount you spent on the horse. It is none of your barn owner's business, and if they need it for insurance, then you can contact the insurance company directly and inform them.
As for the second question, it's pretty standard. Say they can't get a hold of you and your horse requires emergency vet care - you might sue them if they got vet care on your horse if they don't have your written authorization, so this is a way for them to treat a horse if you are unable to be contacted.
**WARNING - if your horse is insured, make sure your barn owner/manager (better, both) knows which company, and who to call to let that company know that the vet is being called for the horse before the vet sees the horse, otherwise the company can refuse to compensate for the claim. The BIG one is for mortality.