Check out the examples i have included that shows you what i like the most. I like the 100% quaranteed symbol of 99design as well.
Cuéntanos a qué tipo de público quieres llegar
The target will be people who come to compare prices for lots of many different products.
I was thinking myself to have the word "preis" (Price) and then the number 1 in a round circle above the word. But thats a idea of mine and since im not so creative i will leave that up to you. Only requirement it should have is that it can be easy to read and the coloring should be liked by each person.