What if it cost $4 - but also gained a copper on gain. That would make it cost less than $5, and wouldn’t be an automatic purchase. The pile may not auto empty. There are other mechanics that could be used to disincentivize if gain a copper is meh. $4 plus a debt, $4 but draw one less card at cleanup, $4 plus gain an estate, $4 but also worth -1vp.
Any of these suggestions probably makes the card even more unattractive than leaving it overpriced at $5. Also, as already pointed out, there is nothing "automatic" about Silver+ at $4 unless one wants to argue that Delve and Patron are "automatic".
Let's also keep in mind topdecking gained stuff is nice but hardly as important as e.g. the Attacks of Idol or Relic, the trashing of Counterfeit or the Buy of Spices and Charm.