Are entrepreneurs that are starting their business really a niche that pays well? Seems like it wouldn't be. Seems like you get either "build me the next facebook for $500" or a lot of small business with a total budget of $5000.
In general, you're right, but there's a sub-niche of entrepreneurs who are either independently wealthy or have easy access to capital that keep all the MVP-building agencies and consultants afloat.
I can't imagine how much work it would be to sift through all the other "ideas people" who need an app next week and then they'll pay you once the cash starts rolling in.
Just bill 50 to 100 percent up front.
Is this typically 5k to 20k engagements over a period of 2 to six weeks?