You already have it. Musk's earliest promise of a $30k price point appears to be an interview in September 2009: https://www.wbur.org/onpoint/2009/09/25/teslas-elon-musk-on-...

Adjusted for inflation, $30k then is around $45k now. Tesla sells a Model 3 for just over $35k.

It doesn't make any sense to hold someone to a promise like that and not adjust it for inflation. I think you can legitimately complain that he didn't meet the timeline he was aiming for.