Just calculated what I save on hay using the slowfeeder nets....520lbs a month=10bales=85$ in your case, if you would have fed as I have, free choice.
Difference is, mine are constantly eating, and have no weight problem, and I feed way less grain.
So, let's crunch numbers
A horse can fare well on hay alone, if it's only working lightly, adult, and hay quality is good, which yours seem to be.
They need to eat between 1.5 and 2% of bodyweight.
Guessing here, since I know only breed, not height and condition, the Arab should be around 800, the paint around 1000, and the draft let's say 1400lbs = 3200.
That comes out between 48 and 64lbs of hay a day for all three together.
You're feeding, currently, at the lower end of these amounts.
Keep in mind, tho, these are numbers for hayfeeding ONLY. No sweetfeed necessary.
If everything was perfect, all you would have to add is salt and a vit/min supplement.