Since there are millions of 3-cent stamps in the world, their values are not high. Collectors usually price them at less than $50. However, some rare ones have a value of up to $1 million.
If you want to sell your 3-cent stamps, clean them and remove any paper or glue that might cause the stamp to stick to the page. You can also clean the stamps by using specialized stamp cleaners. You can also sell your 3-cent stamps on eBay or other auction sites.