oh hey, moat is my least favorite card too! but instead of adding a +buy, I think it should be:
toll moat - $2
+2 cards
+1 coin token, which can be spent at any time
when a player plays an attack card, you may reveal this from your hand. If you do, you are unaffected by that attack.
... to fit with the theme of guilds.
but really, I pretty much never buy moat. watchtower is almost always wayyyy better..... and only costs one more. watchtower draws at least 2 cards (edgecase: CR, Governor), is actually better than a moat against cursers (trashes the curse, lowering the pile. this isn't always good though.) It lets you draw the cards back against discard attacks, and also has cool top decking powers. (also, goons and DA cards w/on-trash effects.
But I guess watchtower isn't always in the kingdom... still, I hate moat.