Mike and his friend worked out the＿＿（开销）of the trip．

expense

比如：
The real cost on car-making isn't design or raw materials, but the expense of tooling up.
造汽车的费用不在于设计和原材料，而在于安装生产所需设备的开销。

Such administrative overhead in a business is analogous to the cost of government in a nation.
一家企业的行政管理性费用与一个国家政府的开销是类似的。

COST
EXPENSES