It really depends how complex you build it. If you just need a CRUD without any complex server setup, scrubbing, etc. you could probably build it for 10-50k, but this amount can 10x or 100x easily if you need more complexity or hire bad developers.

I’ve worked on a for a yelp competitor before and I’ lm guessing they spent a few hundred thousands dollars on it, maybe more if you include marketing and advertising.

Majority come from money or have family that would support them. Thats how they got into entrepreneurship in the first place, it allowed them to take on more risks.