Actually, I have no idea how cheap a "bag of bricks" are, but if it costs more than $10, than these LEGO games are definitely cheaper. Amazon has LEGO Batman, LEGO Batman 2: DC Super Heroes, LEGO Harry Potter: Years 5-7 and LEGO Harry Potter: Years 1-4 all available for digital download for super cheap prices.
The cost ranges from $4.99 to $7.49 with a bundle available that includes everything but LEGO Batman for $13.99. If you're looking to beef up your local PC co-op collection of kid friendly games, this might be the way to do it. All four games feature two player local co-op with game pad support.
Grab any of them at Amazon and support Co-Optimus in the process.
Source: Amazon.com