hrmm... I'll have to ponder that a bit.Your safest bet is to get the basic version from Amazon for 6.99$. But it's also on a number of those casual gaming portals... new customers can have it on BigFishGames for 2.99$.
That model kind of makes sense with games in this genre as you're unlikely to replay them much, but based on my experiences with the demo, I wouldn't trust Alawar.Another option is Alawar itself, they use a subscription model which gives access to the entire game library for a limited amount of time.
The daily pass is just 1$ but you'll have to remember to unsubscribe, or it'll automatically turn into a monthly sub.