Let's look at this from another angle.
First, assume a player is not a "can't miss" 1st or 2nd round selection. (Those players have a chance to rocket through the system, and are handled a bit differently by organizations, when compared to most later picks.)
Compare the rest of the HS picks career trajectories to the highly drafted college junior.
Draft year (year 1): HS (18 yrs) player drafted and heads to complex ball; college player plays local ball in his summer before college.
Year 2: HS player (19) reports to ST, and is assigned to . . . complex ball; college player as a fr gets some playing time and then heads off to Summer ball.
Year 3: HS (20) player has played in instructs during the fall and reports to ST. Gets assigned to SS - play begins in June. College player (now a rising junior) got significant season playing time and now off to Cape or Northwoods (where the feeding frenzy begins).
Year 4: HS player (21) heads off, most likely to SS though a few - if successful and having caught the eye of management - may head to full lesson low A. College player (now a junior) burnishes stats and is drafted. Assigned to SS (particularly true of pitchers who were ridden into the ground), then to instructs.
Year 5: HS player (22) to high A. College player low A with chance to be promoted to high A sometime during season.
From a career perspective (assume the players are equal in potential and current level): HS player is one level ahead, and has pocketed and begun using his bonus money (or mom and dad are paying the upkeep) for 5 years. Has no education but the right to draw upon the MLB college money at some defined point in the future - and which money is fully taxable (thereby diminishing its true value), while college costs has gone up (at least five years of increases, maybe more, further diminishes the MLB scholarship value). Gave up his last chance to be on a real baseball team which plays as a team to live alone in a world which treats him as a piece of meat.
The college player has two seasons of summer collegiate ball (combining the college season and summer leagues provide many with a free taste of the incredible grind of proball; some don't like it); three seasons of being a "big man on campus", three years (for many, however, two years) of college credits, and three years of growth opportunity in the "half-way house" of college living (on your own, but not quite). The MLB scholarship fund is still available (though for only one year and the player will be short of credits and need to self-fund the shortage; but the MLB scholarship amount will be more to cover those increased college costs).
Certain scenarios are very suseptible to mathematic type analysis, such as which mortgage to take. Here the money becomes a minor element - only in the fewest of cases of huge bonuses does it rise above that (IMO) - the other variables (maturity, desire, options foreclosed, etc) cannot be quantified but are far more important in trying to parse the future.
Pro ball is a life style choice; the players in those first years are meat, every day is stressful, it is lonely, it is dull and intellectually lifeless, players have no safety net, no escape, no identity except baseball, ruminating about that last bad start. Please show me an equation which peers into the future and quantifies that. (Just reading this board demonstrates the incredible jump from HS to college and the bumps and dips experienced by great HS players; it is orders of magnitude more difficult in the HS to proball jump.)
Parhaps, a better question would be: will I make it to MLB if drafted out of HS and not make it if I wait and get drafted out of college. Those different results are stark. The issue should not be will I get a shot at proball; rather will I make it all the way? (Sort of like, if a kid should apply ED rather than RD because ED provides a tangible advantage.)
In hindsight, I look at my economic analysis as done more for me, than for my son. It was a framework to try to work through an issue which has so many facets that we needed to start somewhere. But, (jmo) the intangibles make any analysis based upon economics seem unreasonably exact and scientific. I knew none of this while we went through it - I had no clue what HS draftees went though and what they gave up.
I have heard it said, and believe it, that a paycheck is a source of dissatisfaction, not satisfaction. In other words, if you don't like what you're doing, money doesn't make you enjoy it. A million dollar bonus is not going to make a kid mature who wasn't (think Matt Bush and his first spring training), is not going to make a kid use his mind by reading a book while everyone else are telling lies and swapping stories, is not going to make him happy because he has a fat bank account managed by a skilled asset manager. This life decision - and it is a life decision which absolutely forecloses options - cannot be boiled down to dollars and cents.
(Keep this in mind: the player needs to play a certain period of time to (a) not be forced to repay a portion of his bonus and (b) to be eligible for the MLB scholarship money. I know of many kids who - for personal reasons - quit before the time and forfeited all.)