I feel that the closest comparison to an existing card is Stables. The best case is a Lab with some (here, a lot of) additional cycling. It's harder to keep going if you only want to discard junk to it, but really easier as you can discard anything you like. In large numbers this is probably even closer to Lab than Advisor is (as you have more control), but the first few are probably better than Lab, as you also get to swap out some Coppers or Estates. So it might be a tricky card to price, although $3 is almost certainly too low.
What am I supposed to discard if I do not have two identical cards?