I bought this pack that included hot-pads and hand towels at Walmart for 5.96.This could actually make 2 of these aprons as it came with 2 regular hot pads and not just the one that is pictured on their site.
I also bought my ribbon there.
I measured the neck ribbon and the waist ribbon while the hot pad was held up to my daughter leaving enough to tie the back and also enough to add a sticky Velcro to the neck. I would suggest sewing the Velcro also in case you want to wash it. You could also make the waist so that it was Velcro. I like that it ties in the back though as it makes it easy to adjust it on her. The bottom half of the apron is one hand towel cut in half.