If I sell 10% of my wholly-owned LLC to an active member, how do I value 10% of the ownership?

I have foregone a 80K non-profit salary for six months and spent 10K in expenses. I have had everything I own at Risk. I'm considering selling a 10% active ownership to someone who is actively helping me with the launch (this is a no-risk proposition for them, gain only.) How much should I value the 10% at? Our for-profit will be managing 25MM worth of projects, year one...with sizable increase in years to follow.