If we use Travelling Fair as a benchmark for the shadow price of an extra Buy you need to buy 2 cards to make up for the paying of Decadent Nobility and once you buy 3 you got the extra Buy for free. So at the first glance this seems OK for a one-shot Princess.
But due to the trashing this basically sucks. If you already got a megaturn this is unlikely to matter much. As you gotta trash everything that you buy afterwards this is only good for piling, Groundskeeper, Conquest and Goons.
Yeah having considered it more carefully I tried to delete this. I'm not sure why it didn't work
Just because the first attempt didn't work out doesn't mean that your two basic ideas, Princess as an Event and gaining implying forced trashing, aren't unique and interesting.
I agree. There are some interesting things to explore here, even if the original concept doesn't quite work.
If we take the first interesting idea from the card, maybe we could do something like this:
Event - $0
+2 Buys
Once per turn: Until end of turn, all cards cost $2 less, but not less than $0. At the start of Clean-up this turn, take 6 Debt.
I added the Once per turn to prevent total blow-out of the effect, but I think you still get a lot of benefit from it (I suspect that this wording is still too strong and you would always open with it, but there's still room for adjustment).