I used to sell above ground pools. The cost varies dependant upon brand, size, etc.
I absolutely hated selling them to my customers, and tried to discourage them from purchasing them, because they are a pain to take care of.
First you have to decide where you are going to place the pool. That is the easy part.
Then you have to prepare the ground. This is the hard part.
You have to remove all the grass where you are going to place the pool. Then you are going to have to remove approx. 3' more around the pool. You will then have to get the area level.
After getting it level, then you MUST kill all the grass around that area you have just cleaned off, because of the roots.
Then you must make sure it is still completely level.
The reason that this all MUST be done is grass can grow up through the liner, and the liner is the most expensive part of the pool.
Also it must be level because if its not the skimmer wont work correctly.