If I had a dollar for every time somebody told me I could make a fortune selling my quilted items and other fabric crafts....well, I'd have a whole lot more than I ever made actually trying to sell them at a fair price! I found, over and over, that people have a habit of saying things like this, with no intention of every spending any of their own money buying such items. It's always other people who will buy them! In my case, I finally gave up and make what I want, when I want and give them away. Much less stressful. Don't underestimate the stress you will feel at trying to please the public.
Oh, to answer your question, I would pay around $1.50, maybe up to $3 if I was craving a cookie. Maybe even more if it was a very special occasion and you caught me at the right time. But really, like some others here, I would value the taste of the cookie over the decorations, and be more likely to buy plain, but great-tasting cookies, over more expensive fancy looking ones.