Something to keep in mind. Not all rings are created the same: some rings are going to require extra work / money to get re-sized. I specifically wouldn't cheap out on wedding rings with diamonds mounted inside the ring. Dont want to loose on of those sucker one day.
The cost to resize a ring is usually free when you first buy your ring. If you have had your ring a while and need it resized the cost will depend on if you need your ring sized up or down. You can find more information here: http://www.helium.com/items/238839-how-to-resize-a-ring