I would like to know cost for americans in london,going home to america cost
And the of visa stamp please.. synthia

Visa stamps generally don't cost anything. If you are an American in London, you don't need a Visa to return to the US.

As for the cost of travel there are any number of websites where you can look up airfares. Airfares will vary depending on when you fly and what airports you fly from/to.