Overpriced assets?

I think you are wrong. There a plenty of free models and stuff, even on the marketplace available that suffice for prototyping. Assets that I buy on such a marketplace I use solely for stuff I plan to release to at least make the money i spent on them back. You dont have to buy anything stuff, just to play arround with the engine. The engine comes with tons of free assets from all the example projects that are more then you will ever need for prototyping imho.