You may still have a little luck. If it's been no more than about three months since your sales call, and that call was directly through HughesNet, NOT via a retailer/3rd party seller, the reps may be able to pull your sales call to have it reviewed. They are very honest with their sales call reviews. If its determined that you were, in fact, misled, there may be recourse. That recourse if often in being able to cancel the service with either a reduced, or no, Early Termination Fee. I'm not sure about the equipment though, in cases like this, as in what happens to it, or whether there is a refund.
The primary advantage of purchasing the equipment instead of leasing it is that you don't have the monthly lease fee. Some people feel the long term financial advantage of not having to pay the lease fee is worth it.
A 24 month contract, as you've discovered, is required whether leasing or buying, but again, the sales call review may help you, if it was through HughesNet themselves.
Good luck. A rep should reply within a day or two.