The only alternative i know of is Sodium Molybdate (only 39% Mo)
I wouldn't leave it out anyway, because if missing you'll most probably have Mo deficiency. The chances that it is contained sufficiently as a polluant in other components (you may use) is rather low.

The price of 44 Â for 100 gr is acceptable, I paid the equivalent of 15 Â for 30 gram. Try to get a smaller quantity or share it with others. 100 gr is enough for about 800- 850.000 liter!