I think it's well priced as it is right now.
Making it cost $3+P makes the non-Potion buy more critical, like the obvious Silver or some other $3 terminal Silver.
You really need that extra cash, because getting stuck with $2+P is really harmful.
Make it that cheap and it becomes a bit too easy to pick up, imagine drawing $7+P with 2 Buys.
With Familiar costing $3+P you only get a measly $4 card with it, instead of say a Hunting Party with the Familiar.
I often think of Potions as $2.5, but that's mainly because they cost $4, the Potions have a drawback that you can only buy Potion-costing cards with them and you can only buy one such card with every Potion, which makes them closer to $2 for me. Well, this puts Familiar at about $5 while I think it's slightly better than a Witch. Making it a $4 and putting it in the same range as Sea Hag is absurd, because it's way better than Sea Hag.
Nah, I like it how it is.
Now, if they'd make Adventurer cost $4, someone might even buy it!