Calculate how much spread I pay in dollars

Is there a way, using the information below, to work out how much I will pay as spread when I buy a CFD for a commodity or an Index, ie Corn or S&P 500, or AUDUSD?

For example I want to buy $4000 of Corn and sell-buy prices are 377.78 and 378.68, which means spread is 0.90.

How can I calculate what I will pay for spread, if I bought $4000 worth of corn?