If folks don't know you're selling, they're unlikely to buy from you. Many photographers send out promotional mailings, which, besides postage, have costs for design, printing and possibly for purchasing a mailing list. There are also Yellow Pages ads, other directory listings (online and in print), business cards, pricing brochures and special portfolio production costs. Costs of putting on a special show of your pictures might go in this category. Some businesses in some markets also benefit from newspaper and/or magazine display and classified ads. Some folks budget a share of revenues toward this. Consider the same. But forget about being successful without tooting your own horn at least a bit.