Hi JonetteA,
I'm not sure how much the costs would vary based on location/vendor and what you want screen printed, but when we looked into it for our professional organization there was an initial set-up fee (for your pattern, etc.) of about $100. Then there is about a $3 minimum charge per item to be screen printed. There may also be a minimum number of items you must order, and then there is the cost per item.
Hope that helps some!