Trivago is the best site for hotels in my opinion. It searches all the Online Agencies plus the hotel's own sites.
It has some great filters too.
I've already booked my hotel room at a cancellable rate. Agree that there is nothing in the area although my hotel is in Poblenou 40 mins walk so just about doable if there are issues getting on the bus etc. Not the cheapest rate but a twin room so splitting the cost unless my mate bails!
There is a travelodge in Poblenou whose rooms should go on sale on those dates soon so you could keep an eye on that.
Otherwise I'd do a Trivago search setting filters to within 1 mile of the Plaza Catalunya which is where the shuttle bus goes (or used to go when i last went).
Another tip for those who travel a lot - if you use Hotels.Com (which is competitive) and book 10 nights you get a free night equating to the average rate between the 10 bookings.