I have a 2405 and a 3007 and cannot fault either. With the 24inch Dell I have seen the price fluctuate as low as £469 inc vat on overclockers and go as high as £859 the next week, my 3007 was, at the time, a bargain £941 (which I do consider a bargain for a 30" screen)
On the 1x24 or 2x20+ I'd say it depends what you're doing, in the office now I have 2x19s and I like the fact each screen is dedicated to a task/window. I couldn't switch back to a single screen regardless of size. At home I play games, so that is somewhat different...
This ebay bargain tho, does seem a little on the cheap side...