If you want to fly to London cheaply, and you don't mind slumming it, you may want to have a look at Ryanair - they fly from BLQ to STN.

I would second Travelodge (travelodge.co.uk) for accommodation - if you book well ahead you can often get rooms for less than GBP 30 (non-refundable). Their rooms come without phones and without toiletries (apart from a small bar of soap) but are otherwise perfectly acceptable.