To add some additional context, the closed beta users knew from the beginning that the product would be paid after the closed beta. Some even asked about the price, and I gave them a ballpark figure, and all of the responses to the figure were positive. However, once I made the official price announcement, a few people were pretty angry (ironically, some were people who asked about the price and were ok with it at the time).
So I'm not necessarily moving from a free product to a paid product. It's from a paid product that was subsidized, to a paid product that is not subsidized. But to your point, I think the closed beta ran too long and shifted their psychology about the cost of the product.
What if during the sign up stage, you actually show the current price of the free plan. But then give a 100% discount for a certain period. Afterwards, you would then reduce the discount X percentage until it's fully transitioned into a paid model.
If it's all transparent, maybe that would make it easier for people to know that it's not free for free sake and plan accordingly.
That necessitates actually having a price point nailed down prior to accepting any sign ups. Some people (including possibly OP) get the ball rolling without even having a reasonably narrow ballpark guess settled on.
I think you need to study companies that transitioned from a free to a paid product rather than compare yourself against businesses that increase their regular sales through free samples.