Even though I'm not in AZ I tend to try and predict hay usage. The last horse I manages went through 7300 pounds of hay in one years time, that was 20 pounds per day, he was just under 1000 pounds, I think he was 925-950 pounds, if I can remember correctly.
That's just over 2% bodyweight per day and he had nearly year round grazing. I always round up, so 4 tons (8,000 pounds) were shipped in just in case. Extra hay was not needed in the winter either as he wore a blanket and was stabled at night.
So I'd likely try for 2.5 to even 3% (depending on what your winters are like there, I have no clue.) and then round up to the nearest whole number just in case you have trouble getting more hay you'll have some to tide you over.
And just because I saw the prices listed, I spotted 40 pound bales of alfalfa for sale here for $23+ dollars recently...I just about passed out. I can go to TSC and get 50 pound bales of alfalfa for $18 and it looked and smelt better.
"They see me rollin, They hatin, Patrolling they tryin to catch me ridin dirty"