You should be able to enter all the info in online without having to send it that way and get an amount, I don't know if it will be the same though. Just think of it as what you are willing to pay for the transfer plus a swift kick in the balls.
Depends on the exchange rate for where you are sending the money. Europe will cost much more because their dollar is more than the US dollar. But if you send to China, it will be much cheaper. Also, each WU location charges a fee for using them. But $20 sounds reasonable.