Ok, I don't know relative pricing in other countries, but periodically Ghost Squad and HotD2/3 drop to $15 each (new), and the plastic attachment can either be bought with Zelda's crossbow training $20 new, not on sale.
HotD2/3 isn't all that good, either - the games aren't updated with anything, it's just a straight port. And I thought HotD1 was better than 2/3. HotD: Overkill looks like it'll be absolutely astounding. As for Ghost squad, it looks good but I haven't played it yet.
For the money, I'd pick up GS/Zelda and wait for Overkill unless you're really into HotD2/3.