<a href="http://www.ladders-online.com/Ladders/E
xtension-Ladders-Trade">Trade
Extension Ladders</a> are nearly as cheap as DIY ladders. 2 section ladders are longer than 3 section ladders and will flex less. But trade 3 section ladders are very stiff and you won't notice flexing. To use a ladder safely you should use a <a href="http://www.ladders-online.com/Accessori
es/Stabilising-and-Securing/LadderMat">ladder
mat</a> that will stop your ladder slipping. I agree with Ian, don't go cheap.
Nicola.S