how to determine cost savings based on resource utilization

First off, I'm not even sure how to ask this correctly so bear with me
lol.

I'm trying to convince the powers that be to allow us to modernize (or at
least update) our custom code. We still have a ton of old RPG 3 (written
more like RPG 2) and way too many CLs using OPNQRYF, etc. and the question
is how is it possible to quantify this in terms of $$$. I know that I can
come up with a semi-decent guess as to man hours saved on program
maintenance but I can't even hazard a guess as to how I can calculate the
reduction in resource utilization, response times, etc. does anyone have
any ideas or methods they have used to try to at least get some inkling of
the savings of modernizing? We are currently migrating to a web based
financials (with the added bonus I get to at least do some cleanup on the
interfaces for some of this jalopy code). Since I have a small bit of
leverage during this process and we are in a holding pattern with the
vendor I'm trying to get a consultant to work on updating the existing
code to use modern techniques (i.e. Service programs, SQL, etc).

Anyway if you manage to decipher that long-winded diatribe & have ideas or
suggestions it would be MOST definitely appreciated!!!


Thanks,
Tommy Holden