以上四个词和“消费”、“花费”和“消耗”有关。
●首先，spend主要做及物动词使用，其宾语可以是“钱”、“时间”或“精力”。
Every year, she spends a lot of money on clothes.
女孩，您用生命买衣服啊。
We’ve just spent 1.9 million on improving our computer network.
笔者回想起在老东家有一段时期几十个电脑共享1MB带宽的工作环境，何其辛苦!
I’ve spent an hour in the station waiting for the train.
各位瞅仔细了，spend [money] on doing sth.但是spend [time] doing sth.这就是区别。雅思考官各个鹰眼犀利，可别范怂。
My sister always spends ages in the bathroom.
我姐姐洗澡总是洗很久很久。
I want to live in a dormitory to spend time with my school friends.
For the past month, he’s spending all the energy trying to find a job.
此外，spend并非大家想象的只能由人或机构做主语：
Her anger soon spent itself (=stopped). 她只生了一会气。
●expend的用法和spend差不多，比expend更为正式，可以用于雅思写作;
You expend so much effort for so little return.
你还真是入不敷出。
Governments expend a lot of resources on war.
政府在战争上投入很多资源。
●cost的用法与spend, expend不同。cost的主语一般是花出去的钱、时间和精力的对象。
I cost 30 dollars for the board game. X
The board game costs me 30 dollars.√
I spend 30 dollars for the board game.√
One costs more money running a business than buying a house. X
Running a business costs more money than buying a house.√
It costs more money to run a business than to buy a house.√
(因为这句话的主语是不定式to run a business，所以它被放在谓语和宾语后面，主语用it代替)
●pay的用法。pay强调“付款”，也有pay [money] for sth.这样一看就懂的用法
You have to pay four dollars for each hamburger.
当然pay还有很多其他用法。
Mum paid for my driving lessons./Mum paid me for the driving lessons.
妈妈帮我付了学开车的钱。
Ray paid some kids to wash his car.
Ray花钱叫几个小孩来洗他的车。
Ray paid the kids 10 dollars to wash his car.
Ray花10美元叫这孩子洗他车。
A savings plan that paid six percent interest
一个6%利息的储蓄方案
It pays to be honest. (= It is good to be honest)
William is now paying the price for his early mistakes.
威廉姆现在在为他之前的错误买单。
I decide to pay my folks a visit this weekend.