There are plenty of marketing schemes that are being used nowadays. The most commonly seen are ads by the use of hoarding and billboards. But ads through these are so large and they are not the type that can be carried around unlike custom flags.
Custom flags are marketing materials that are used in the past for promotional campaigns and other events. This is one of the most basic yet effective schemes to market something. It does not need a big budget to have this kind of marketing material because it is made by simple materials such as fabrics, prints and a good kind of pole to put it on. It is no brainier to think and compare the price difference between a billboard, electronic ad and a custom made flag.
You can go through your yellow pages or search in the web to find printing agencies that offers or specialize on supplying custom flags. They offer wide selection of flags according to what you want and depend on your needs and purpose. They can make the design for you but that may have an additional charge. The printing cost will depend on the type of materials, size and quantity you will order. The total cost is not fixed, it can still be negotiated especially when you order in bulk.
Be sure to find a reliable printing agency that is known to provide quality product and customer service. If you found a possible supplier via internet, some websites show customer feedback for you to view and refer to.