And it has complex, undocumented connections to north of a hundred other systems. Screwing up any one of which could have hugely impactful effects on the business (or not, who knows?). So you're going to be coordinating testing with 30-40 teams in diverse parts of the organisation (and externally).
And your couple of million won't pay for the redesign of all those feeds. Hopefully they won't take the testing costs out either or you'll be broke in 2 years.
See, the thing with extracting these old, large systems isn't really the language they're written in, or the hardware they run on. Though those are nasty, ugly problems. It's the coupling. What will almost always defeat you, unless you give the problem the respect it deserves (and often even then) is the coupling.