Not bad:


Motor - $29.99
Battery - $34.99
ESC - $34.58
Charger - $18.99
Misc connectors - $9.00

Or $127.00 for the conversion.

Assuming you pick up three more packs @ 34.99/ea

Your total will be $232.52, but the packs will be usable on other planes, and you can charge the first used one while you fly with the others.

Since it is a .40 size plane, you could also use a less powerful electrical system, and reduce the cost further while still getting great performance.