I was thinking about finding out more details about the project initially since I have a ton of free time, but that "any changes that we felt were needed" claus

I was thinking about finding out more details about the project initially since I have a ton of free time, but that "any changes that we felt were needed" clause sounds fishy. They seem to want someone to build the prototype, then re-build it. Why don't they just design it right in the first place? And paying only $500, and keeping all the rights and IP to boot? Nah, I need cash but not that bad.