Ecommerce for 1 item

Ladies and Gentlemen,
I am fairly new to designing WP sites, and enjoying very much , the ease, the community, ect. I have a client that is wanting to offer a coupon on his site. So I am looking at only one item to sell using a credit card…what would be the simplest way for my to do this as I have yet to try to set up an e commerce and am frankly a bit scared to do so…any thoughts/directions would be appreciated. PLEASE note- I am not a designer by trade, but a Professional Photographer, and have fallen into web design quite by chance, so anything beyond the most elementary code writing is beyond me.

THANK YOU!
Tim