the estimated spend for Q3 is a million dollars.
It comes from the verb spend and according to the Oxford English Dictionary, the noun (the action of spending money or the amount spent) has been used since before 1688, in The works of John Bunyan: with an introduction to each treatise, notes, and a sketch of his life, times, and contemporaries:
What if I cannot but live upon the spend all my days, yet, if my friend will always supply my need, is it not well for me?
Or, specifically as the amount spent, the earliest quotation is from 1976, in Computers in Higher Education & Research:
About £21 million should be spent for universities on new machines, buildings and operating costs..with a spend of about £10 million for research councils for similar purposes.