Here are a few American phrases:

1.) A sledgehammer to crack a nut – means to use disproportionate force or expense to overcome a minor problem.
2.) An arm and a leg – The cost is a large amount of money equivalent to the cost of an arm and a leg
3.) As easy as pie – means a task is very easy to do.
4.) As happy as a clam – this expression means for one to be very happy and content.