this is a horrific deal in many ways. Now, there is not enough information provided, ie, cap cost and the money factor that you are paying to determine how bad of a deal it is. But let me give one possible scenario of what the dealer is doing.

At an MSRP of 57k
Cap Cost 57k (you are "buying" the car at MSRP)
Cap Cost reduction of 4k
Dealer upcharge of .5% on the APR/Money Factor
Residual of 59% based on 36 months (current OCT rates)

You payment should be 737.30 plus tax.

To be honest, I can't even fathom getting to $900 without the dealer selling you the car for 4k OVER MSRP and adding even more of an upcharge on the Money Factor.