To find out how much a business is worth, you should start with your own accountant who can give you a good idea based on a review of the financials. Or another low-cost option is to contact the Small Business Development Center which offers assistance with business valuation, market research, business plan, and projections.
You could also contact a CPA who will want 2-3 years of business taxes, Profit and Loss reports, and include the Balance Sheets. The CPA will only be looking at numbers (revenues, debts, assets) and will not consider the market or other outside factors.