I don't have any useful advice to offer, but perhaps some clarifying questions are in order. Frankly, some of what you've written here seems to me to not square up with some other parts. Probably you'll get better and more informed opinions if you expand a bit on these.
For example, the statement that the player is ready to immediately play at the AA level seems incompatible with a ranking (by PG Cross Checker?) outside the top 100 high school players. From my point of view, even if no college or JC players were involved in the draft, the number 100 player would be drafted in the 3rd round or lower, and when we take into account that more college players are drafted than high school players, the 100th best HS player will be at best drafted in rounds 6 through 10. Sure, the folks doing the drafting may hold a higher opinion of the player than PG, but it won't be much higher. I don't see how such a draft position presages a placement in AA ball.
The same conclusion can be reached by ignoring draft possibilities and simply considering the talent pool available to play AA ball. A player isn't just competing with other players who signed in the same year; he'll be competing with players signed over the past 5 or more years.
Or you could just look at some AA rosters and note how few players are one year removed from high school.
You mention that he is "being heavily recruited by the top D1 universities in our area", but seemingly there are just two offers under consideration. (Just two offers in August is a dilemma most players would love to have!
) Perhaps there will be other opportunities which may have adequate prestige and a lower financial expenditure?Finally, are you expecting that if he signs with the more prestigous college, he'll have a higher draft postion next June, or after his junior year of college, or both? My own uniformed opinion is that it won't affect his draft position at all, although the financial worth of a college scholarship may affect the signing bonus out of high school. For a player drafted out of college, I think that the player's performance (which is likely affected by the "fit" of the player and college) over the next 3 years far outweighs any prestige effect.