Poets Quill is basically the same card as Shadowspear, but as a cantrip its significantly more exciting especially when the card you find is always a creature if you need it
In practice I think different colours gain more or less from lessons more as a result of their colour pie and cube archetypes
Alternatively, if youre playing a Treasure Tokens matters deck, Ruthless Technomancer can create 10,000 Treasure tokens by sacrificing Jumbo Cactuar
The list includes favorites like Gemhide Sliver, Harmonic Sliver, and Might Sliver, but dont sleep on some of the grindier cards like Darkheart Sliver and Necrotic Sliver, the latter of which can find a home outside of tribal decks as well, like in a Karador, Ghost Chieftain build
I think the price on these 3 cards is more or less correct which is why I used them as a reference