First time you play this, you trash a copper for $0 essentially. Second time, you do it for $1, then for $2, then for $3 and so on. Eventually you'd need to start putting silvers on the mat but whatever, you can still even just play it for the +buy.
The main issue I can see is that it's far too strong a strategy to itself. The most powerful thing it combos with is more War Chests (probably), and with 2-3 of them going through your deck, you'd easily get a card giving obscene amounts too quickly. But it's REALLY hard to judge - in a quick game, it's probably bad, as it won't get up to value quick enough. But in a slow game, it'd be incredibly strong. I think that swing is probably too much, and I think it leans towards the latter too often.