After a long period of deliberation, I have decided that terror-watt is not the worst effect in the game.

Sold for a Miami Nights Human Cannonball(25.5 Keys, round to 26)

http://backpack.tf/profiles/76561198262422109#!/compare/1490918400/1491004800

Sold for an Orbiting Fire Modest Pile of Hat(27.5 Keys, round to 28)

http://backpack.tf/profiles/76561197970869719#!/compare/1491177600/1491264000

Sold for a Disco Beat Down Conquistador(20 Keys) and a Kill-a-Watt Gym Rat(10.5 Keys, round to 11)(31 Keys total)

http://backpack.tf/profiles/76561198107520045#!/compare/1490572800/1490832000

26-31.

Credits to Mindacos for finding the proof. All I did was make the actual suggestion.