Almost anywhere around Canary Wharf is going to be pricey.
The Britannia International Hotel (which is just under half a mile from Canary Wharf) has a 'rack rate' (i.e. what you'd pay if you just turned up without a booking, and didn't haggle) of £255 per night but they're currently offering £88 for that Sunday night if you pre-book:
http://www.britanniahotels.com/hotels/london
Even better, you can get that down to £75 if you book through this site:
http://www.hotels-lon...a-international.hotel
The CityStay Hotel
http://www.citystayhotel.com/
is offering £49.90 per night when booked through that site:
http://www.hotels-london.co.uk/citystay.hotel
It's about one and half miles from Canary Wharf but you'd simply need to stroll down the road (to Bow Road station) to catch a DLR train to Canary Wharf (which is 5 stops along the line, with trains every few minutes).
Chris