Your marketing efforts do not have to be expensive. In many cases, companies that don't have marketing plans spend more than is necessary to reach their customers. With a plan that will spell out the ways you will market your company, you will save money and energy on your business marketing efforts. Creating an effective marketing plan is one of the most crucial elements of planning for your business.
Another consideration. Should the business plan be a document that is focused on selling an idea for a product or service? For many years I worked in a company that did not want anything in a business plan that could be construed as showing a bias towards or against a project. The mantra was to only present facts in the business plan. The Operations Research Department was there to review the analysis as being unbiased. To handle the "what if" scenarios or sensitivity analysis we prepared a supplemental analysis documents which were mostly financial oriented. Personally, I like a factual approach and use the presentation of the final document to point out the conservative aspects of the content.