Currently Ladybird has 200k USD from FUTO, 100k USD from Shopify and then a bunch more from ProtonVPN, Ahrefs, etc., they also have 7 full time employees and a bunch of volunteers: https://ladybird.org/#faq
They fall short of the numbers you suggest, but it's kind of encouraging that some people can do that for an entirely new project. Time will tell how it works out for them, but I could feasibly imagine a Firefox fork gaining similar ground, should people get tired of Mozilla's stewardship for whatever reason.
After all, even something like 3% of the market share is way more of a proof of feasibility than 0% and if you get a bunch of money when that figure is 0% like Ladybird, things can only get better for a project built on established technology.
Good for Ladybird, but I don't think they can support all the complexities of the Web with only 7 develops (but perhaps with enough volunteers they could - 7 is enough to do the hard thankless work while volunteers do the more interesting bits). Between all the weird layout rules, required speed to be useful, and security (last only because with out the other two you automatically have perfect security since with no users holes cannot be exploited).
If I had 7 disposable engineers, I'd built an open source modular browser that allows individual components such as rendering engine, JS engine, WASM runtime, etc. to all be swapped out for alternative implementations. The browser itself would basically be a shell and SDK. It's ludicrous that someone has to either completely reinvent the wheel today or fork one of two monolithic browsers that require significant upkeep and cross-domain expertise.
I feel like this approach has a much better shot at being sustainable and giving power back to users and clients, despite having its own challenges. I would like it if political fallouts such as this one didn't mean I have to completely migrate to a brand new system. Compare that to Linux, where I can say, migrate to Rocky if CentOS stops being a viable choice, without losing any of my tooling or configuration.
it need not be money a dozen developers donating code full time would work but that is harder to get.