Does anyone know of a good site to make a professional-looking, personalized "gift card"?

I want to give my sister a “coupon” for a matching necklace set for her and her doll, but she gets to choose the style and color of the necklaces and I’ll make them for her. I want to make it look professional and stuff, maybe make it look like a gift card to a real store. Any ideas for some sites? I would prefer it to be low-price. Thank you so much!