I'm sorry to come in with a blatant promo, but we've just done exactly what you described! https://www.taxaroo.com.

We can match you with a preparer from anywhere in the country, we quote you a hard up-front price, and you interact with your preparer entirely online.

My co-founder (a CPA) and I just launched it this year, and we've received extremely strong interest from professional tax preparers. We actually did a Show HN a little bit ago, but didn't get much traction: https://news.ycombinator.com/item?id=11074466

Would love to hear your thoughts!