Well, knowing that you applied to YC in the first place, you must have thought on some level that they are more experienced and/or better at making these kinds of evaluations than yoursel(f|ves).

I would at least be interested, then, to hear from YC why they gave you such a low valuation, just to be sure you're not missing something important. Then you can make you're own decision as to whether YC's logic makes sense or not.