While I'd agree with at least 4, I'd say it'd be way more than that
^^ Even if we go by the average price of 250,000 per shiny which
most shinies don't reach anymore, that'd only add up to 1 mil pd. A
normal ditto is easily worth at least 4 mil pd and can go up to
around 7 mil pd (I've seen it happen although it tends to be around
the lower end these days). It's difficult to evaluate how much a
ditto would cost in terms of shinies such different shinies have
such diverse prices already ^^
As for a shiny ditto, 2 mil pd is a massive understatement.
Considering the fact that a normal one can cost up to 7 mil pd and
the fact that there is no shiny ditto on site that I'm aware of,
nobody knows how much that would go for but it's definitely more
than 2 mil pd.