I've got this 450Nm Clarke 240v corded impact wrench, the only downside is the fact that it's corded, but it's cheap as chips and where i'll be using it i have a retractable extension lead so no drama there!

http://www.ebay.co.uk/itm/Clarke-1-2...item4d004cf84e

It's been great the few times i've needed to use it, probably worth spending more money if you're planning on using and abusing it every day though, as like most things you get what you pay for.