I would consider this a very strong $5.
Consider Embassy. Embassy is only a net hand size increase of 1 card. If you play it from a hand of size 5, you end with a hand of size 6. However, it is still a pretty strong card -- 15/61 in the
2013 $5 list. And remember that Embassy grants opponents a free Silver when you buy it. If it didn't do that, it may very well be ranked higher.
Now Hunter -- Hunter also gives a net hand size increase of 1. It sees almost as much as Embassy -- 4 cards instead of 5. And then instead of discarding 2, you only discard 1 and top deck the other 1.
Nominally, the topdeck is a penalty. Practically, it is often a bonus. Courtyard is a better BM enabler than Smithy. With such large draw in Hunter, you will probably have more money than you need. In that case, you can put back an extra Silver or Gold to improve your next hand. Because of this, I expect Hunter would be much better than Embassy.
Note that it probably shouldn't cost $6 because of Hunting Grounds.