I know my answer, and I'm aware you can find themes for like $20.
The landing page is a single page thing, jump links on the page, then a form to collect an email.
With regard to responsive design, cross browser stuff being a given/addressed... $30K?
Point of this is I'm trying to see if there is any reason to think this is reasonable.
Hosting/certs is a minor concern could be done by you or provider. No changes to the site after it's done.
I would also add that you're a startup/don't have cash flow, maybe some kind of investment/seed money.
Even then, 30k for a single page, which I assume is static, is kinda ridiculous. The only justification I can think of is very, very good design from an expensive design agency.
For the dev work we are talking paying someone $300 / hour for over 2 weeks. Seems out of my reality.