Even the best college ball team is sloppy as hell compared to even a bunk NBA team, and most talented street hoopsters would find that playing on a college squad is a whole different program that's worth putting 20+ points on their team's game. The difference between a typical NBA team vs. the ghetto-ball players wouldn't get narrower than fifty points -- and I'm being damn generous.
RDB3 made a good point here, and one that's entirely believable.
I think you are making a wrong comparison. College ball is not equal to "street talent" for one reason - and that is age. It would be very difficult for an entire team of 18-21 year olds to beat a seasoned NBA team. However, your street talent would consist of guys from 18-40 years old, some probably former semi-pro or college talent.
In addition, considering the recent deluge or high school players into the NBA, many NBA games look just like a pick-up game, with hot-shot behind the back passes that end up in the fourth row. You have probably dozens of NBA players who each have less than four or five years experience of organized ball on a competitive level. There is no doubt in my mind that an organized team of guys in their late 20's and early 30's could beat an NBA team, especially if the refs are going to call it their way.