I have been trying to do something similar for the past couple of weeks. I am basically trying to come up with a formula that best describes a player's value as a number, taking into account their categories (the standard 5x5 hitting cats.). The way I found that mlb.com did it is this:
(R x 5) + (H x 4) + (HR x 15) + (RBI x 5) + (SB x 15) - AB
I used this formula to run over the projections i have each player for the 2005 season. This takes into account batting average by subtracting AB's, while giving 5 points for a hit. There was a bit of contraversy about whether or not the values that the categories are multiplied by are fair. The above equation ranks HR's and SB's are equal, however steals are rarer, but HR's contribute to BA, HR, R, and RBI.
The reason I want to develop a formula like this is simply to rank my position players....by position (ie top 15 1B etc.). What I did last night (but am not sure if it is relevant) was calculate how many of each of these categ. occurred per at bat for 2nd basemen.
Total Runs / Total AB (for 2B players) = 0.0356 (just guessing)
I then used the inverse (by dividing 1 by ^^ that number, 0.0356), and it gave me a value - 28 for the above example. Then I plugged that number into the equation that mlb.com had, and then ran it through my projections for each player, hence giving me my rankings. I dont know if this helps, but it is similar im guessing. I dont even know if what i have done is right, or that I will even run by the rankings that the result gives me. Just throwing it out there....