This may seem obvious, but an important thing to determine for any particular listing is whether or not the seller would be willing to ship to the U.S.A. If the seller is willing, then you still might need to contact him to find out the shipping costs that would be involved. (This would be the case in the second listing to which TheDon linked above.)

Exchange rate? Tom, you've got a computer and an internet connection!

Try typing "1 euro" (or whatever number you wish to convert) into Google and then clicking the search button.