Good Collapsible/Extendible ladder?

I'm looking a good collapsible or extendible ladder at a fair price, that can extend over 20 feet. I've seen a couple 16 and 17 footers, but those don't really interest me. I've only found one 19' and one 21', both at Home Depot and they look pretty good, but their prices are pretty steep (320$ for the 19', 350$ for the 21')..

Any one know where I could find something like this, but a bit cheaper?