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.