You should be getting paid on a continual basis. 100k worth of work for no pay is ridiculous.

I have never heard of a startup exploiting a freelancer this way, but wouldnt be surprised if this happens.

I can imagine unethical startups trying to exploit a developer who is too trusting. Don't be that developer. Make sure to have a contract, and make sure to be paid for it biweekly, or monthly.

And if they don't agree to that, then well, you probably shouldnt be working there in the first place.