Opinions needed

So I'm finally almost through with entering play-by-play info from the 2006 football season, and some time toward the end of next week I'll be compiling some stats to look at before the new season begins. I've been looking at some basic Football Outsiders stats like Line Yards and quality plays, but I'm wanting to figure out a way to weight the costliness of turnovers. I'm not a huge fan of "points off turnovers" for football because it doesn't tell the whole story. For one thing, how close your team was to scoring before the turnover seems just as important as whether your opponent scored. For another, there's no telling how much your turnover actually led to an opponent's points. If you fumbled at your 1, and they scored a TD on the next play, then yes...your turnover played a key role. But if you threw an INT at your opponents' 20, and they just happened to drive 80 yards for a TD, that doesn't say a lot. And if you threw an INT at your opponents' 20, and they drove 30 yards before punting, that's still a pretty costly turnover because you blew a key scoring opportunity.

As I've been entering the play-by-plays, I came up with a pretty primitive equation that simply factors where the turnover took place (3 points if it took place between either your or your opponent's goalline and 20, 2 if it took place between either 20 and 40, 1 if it took place between the 40's) and how close the game was at the time of the turnover (2 points if within two possessions, 1 point if within 24 points, 0 if over 24 points). There's a maximum of 5 points available. If the turnover is returned for a TD, it's an automatic 5 points. That's okay, but it still doesn't really tell the story. For instance, if you fumbled at your 45 and it was returned to your 1, that's 1 point because it took place at your 45. I guess I could simply look at resulting field position to fix that problem...but that would open up the opposite problem (you fumble at your opponent's 1, they return it to the 45...and it's only 1 point). Maybe an average of the two?

Anyway...for all you lurkers out there (our readership has gone up nicely, but the volume of comments has not), any ideas on this? Is there a better way to measure turnover costliness? I'm open to trying anything that can fit in an excel equation.

(Also, if you lurkers out there just wanna say hi, that's cool too.)