Dear,
I'm involved in some very serious MS Project projects as architect for interoperability with other systems. (Now exploring odoo and some BI platforms).
My quote doesn't mean much now, since the overall scope is not known. How much of the "internals" of MS Project do you tackle with your current software?
How much things did you actually implement?
What data are you taking out of MS Project, and how?
How about multiple version compatibility?
How many reports and what type of reports do you create?
I'll be honest... I have over 15 years of experience, and I've seen people (even in Excel) create masterpieces that were fine tuned over their whole career.
So, don't listen to these kids here, maybe you have a real jewel. You probably know your MS Project stuff, and that is actually what you are trying to market.
You should even consider some cloud solution as well to market this (maybe even the best way to go). It's easy to market, whole world is the market, no software installation, etc.. There are some issues with privacy, and data exposure, but still worth considering...
Share some more information, and I'll at least give you my opinion, free of charge :)
Good luck!