I've done consulting for various startups/online businesses and provided exactly what you describe. Spending a couple hours at project milestones to discuss with an expert can make a big difference in clarifying the project so that it continues smoothly and effectively.

Yes, you can figure things out on your own, and while it is great to learn from your mistakes, having a few pointers along the way can save a great deal of time in getting you to that next step effectively.

What type of projects are you looking for a mentor on specifically?