How much should professionals and consultants invest in marketing? That depends on your business goals, but here are some norms. Law firms generally spend about two percent of their gross revenues on marketing, and the average expenditure is about $136,000. Marketing costs for accounting firms average about seven percent to 10 percent of gross revenue (Source: The New York Times, November 15, 2001). The typical architecture, engineering, planning, and environmental consulting firm spend more than five percent of their net service revenue on marketing (Source: ZweigWhite’s 2003 Marketing Survey of A/E/P & Environmental Consulting Firms).