The plan document is important and should have broad readership. The budget, on the other hand, is best managed with a smaller circulation. Budgets for marketing and communications activity can be accomplished in a variety of ways. Many companies simply do the best they can with a ballpark that has been established within in the past two-three years. Consumer products marketers often battle for a reasonable “share of voice” and budget based on best estimates of competitive spending. New products often try to obtain targeted rating points. When all is said and done, the budget should be a companion document to the marketing and communications plan. It should be realistic and fair. The budget also needs to be evaluated quarterly as the year unfolds. My experience has been within a relevant range of a wide variety of budget scenarios. Examples: I was account director at D’Arcy when they rolled out a campaign on behalf of Caller ID in the Pacific Bell territory that totaled $17 Million. Working with Crossland Construction in 2011-2012, I noted a budget for marketing and communications which was decidedly more modest. (Less than one million dollars for a company with annual revenues of $500,000,000. Needless to say, the budget did not match the ambition of that organization’s marketing communication goals.)
Your chief marketing officer (If you have such an animal in your organization) should be able to make a persuasive argument for a budget consistent with your strategic plan. More often then not, however, it is an operational decision. Don't sell yourself short. Make a budget. Build a plan. Use marketing tools to increase your chances of success.