I have a range of products from 20 to 20,000 dollars. I want to be able to have a high markup for lower priced products but a lower markup for competitive priced expensive products. Forgetting tax for now... EG - 5 item cost might get marked up to 10 (50%), but 5000 cost might get priced at 5100 (2%).
If I had a min margin, how would I go about generating a formula like this for use in pricing products, based on cost alone?
There are many formulas. You need to decide what you want. One silly one is margin $=\frac k{\text{cost}}+\min$. Given the minimum margin and the margin you want at any given cost, you can find $k$ and you have a formula. You could also do margin $=\frac k{\text{cost}^{1000}}+\min$ That decreases the margin much faster than the other as the cost rises.
Why should your margin on an object only depend on the cost, without consideration of the competition for that item?