Robert is correct in applying total asset valuation to the venture. It takes all types of assets, money, people, time, facilities, product, management, market share, good-will, customers, contacts, prospects, concept.
And there are several ways to evaluate a venture. There is asset based, revenue based, share valuation (what your shares are valued at in the open market), and variations on these themes.
Many analysts use all three and pick the valuation or average of these depending on what they are trying to do.
Obviously, we don`t know the details of your proposed venture, so forgive me if what I`m suggesting is too simple or you have already done this.
To strenghten your position on the concept, have you done significant market research to support the marketability of your idea, the anticipated revenues, market acceptance, position, share? The more solid, researched numbers you can bring to the investers, the more valuable your concept will be.
To the extent you possibly can, turn the tables psychologically, make them want your idea more than you want their money. You`ve heard the term "opportunity cost", which is a component in evaluating where to put money. Make the opportunity cost for your venture greater than any others they may be considering and you will have your increased value.
I`d love to hear some business analysts chime in on this.
My experience for making these suggestions is in starting and operating companies. I`m an idea guy that has started a couple of companies and am currently raising funds for a bio-diesel operation and an ICF manufacturing plant near Baton Rouge, to the tune of $5MM.