You are asking about what I would call founding/inception costs. I was replying to an
absolutely wrong comment that was about scaling/growth/marketing costs.
From my own experience, I helped cofound a now-successful small business that we retain 100% ownership of. Founders used <1> the “sweat equity” of our own time (even with kids and mortgages), and <2> one person did some consultancy work, and <3> we had one initial large-business customer (although nowhere enough to pay our usual wages, it helped a little).
There is a lot of “bootstrapping-pr0n” videos and websites with a variety of techniques to build a business without extreme inception costs (e.g. techniques to avoid requiring paid staff when starting - staffing being the main cost for most software startups). The fabulously good video I linked alludes to some of that, and you can find other videos from those conferences.
If you do want to get initial funding, I think that ycombinator is an astonishingly valuable deal. Even applying should get you back more value than the time it costs you: https://www.ycombinator.com/apply/
Edit: I strongly recommend you avoid the “go big or not at all” culture/mentality: most founders fail and the median payoff for founders is quite negative. Venture capital and startup-pr0n encourages you to aim for billions: VCs can spread their bets; VCs have asymmetric information and payoffs; VCs only invest in less than 1% of the potential businesses they see; VCs get paid a base rate by their limited partners; VCs get preferential shares. For an individual it is more like a lottery because an individual’s risk profile is absolutely different from a VCs.