I feel like even if this only Exiled a Copper from the supply and not also a Curse; you still wouldn't want to buy this in the opening pretty much ever. Compare to Borrow... they both give you + to spend in your opening; but Borrow makes you put your -1 Card token on your deck as a penalty. Haunted Cruise makes you put your -1 Card token on your deck every single shuffle for the rest of the game (that's basically what gaining a junk card does); and also gives you -1 score.
The curse does not enter your deck, only the copper does. If you want to model it as -1 card, you also have to model it as +1 coin since copper gives you +1 coin. With borrow, you get it once and next turn. With h/c, you get it many times, but much
later since it doesn't affect you until you draw the copper the
next time. Short term, h/c is much stronger than borrow, so the question is how heavily you want to discount.
But the card is not meant to be super strong in the opening. It may be better in the later game when you have thing that interact with the copper, either by wanting lots of cards or by trashing. Say you run out of cards for spice merchant or something. I don't think the situations where it'll be better than borrow will be rare.