I am running a small independent startup myself where I count every nickel and dime. I tried Google Ads (there was an offer to spend $400 to get an additional $400). Besides a few sign ups, it didn't pay off at all. I would never even consider spending $20,000 (!?). I talked with a few newsletters (starts at $1500 per quarter for a campaign) and social influencers (starts at $700 per post) and if money wasn't an issue I would buy marketing, but in the early stage the most important resource is myself. If I spend my savings that I live off, I risk running out of money and must go back to being a freelance developer (and the European market sucks at the moment).