I completed it when I at level 14 and starting with $1650. without any supply/boost. Build a Heli and upgrade it to 1/0 , and then build Spike Factory at the bloonprint. then build a 2-1 glue at the right side and let it can attack the entry point. then two 0-1 ice at the right side (2 corners). and then upgrade the glue to 2-2 and target the last aim. At level 10-13, Heli shall focus on the left side and help the right side if needed. Before the level 14, sell all except the Heli, you shall have $5600+. Build 2 ice on left side (2 corners), a 2-1 glue, and a 1-2 Spike Factory on the top left.