Monthly spend on SEM + SEO?

Hi, I'm curious how much - if anything - early-stage startups are budgeting towards SEM and SEO in their GTM strategy? (Here, I mean early-stage = pre-revenue, first round of pre-seed funding)
If you have a well-structured website (headings etc) a good keyword strategy (check Google trends, SEM rush) and someone to write and disseminate good quality content, I can't see why you would need to put any more money behind it.
Start with a great website and build good content. It also depends on your product, but don't go all out with SEM just yet.