Kids Woot has these K’nex Extreme Ops for $9.99 (Retail $24.99).

Here are the missions available:

Mission: Arctic Quest

-Building set includes 165 pieces
-Includes 3 K’NEXmen, 2 blasters, 3 missiles, a vinyl decal sheet, and a cut-out backdrop on the back of the box

Mission: Jungle Rescue

-Building set includes 176 pieces
-Includes 3 K’NEXmen, 2 blasters, 4 missiles, a vinyl decal sheet, and a cut-out backdrop on the back of the box

Mission: Desert Command

-Building set includes 156 pieces
-Includes 3 K’NEXmen, 2 blasters, 6 missiles, a vinyl decal sheet, and a cut-out backdrop on the back of the box

Mission: Fireforce Resistance

-Building set includes 162 pieces
-Includes 3 K’NEXmen, 2 blasters, 4 missiles, a vinyl decal sheet, and a cut-out backdrop on the back of the box
-Features a real working suspension!

Plus all of the missions can be combined.