Look on travelbookers.com, opodo.com, lastminute.com and see how much they quote for what you want.
Then remember these numbers, or write them down, and go ask your local travel agent for some quotes.
In terms of flights, the only way to fly direct from the UK is with Virgin from Gatwick - I don't know about the cost, but going in September will be a lot cheaper if you can avoid the first week which is still considered the summer season.
There's all sorts of connections you can do if you want to try and fly from Birmingham to the US, but you'd need to look for that one yourself.