Might be worth booking with Premier Inn. The Goldsmith Street one is very close to Rock City. A favourite with fellow NMAers. Yes, it's a bit pricey (I thnk my room is about £80 and I booked that months ago) but bear in mind that (a) you can cancel right up to the gig date if you find something better / cheaper and at least you'll guarantee a place to crash and (b) the price is per room, not per person, so if you're bring someone else it might work out cheaper than a hotel that charges per person. Be warned, if you're coming with someone you don't want to share a bed with, it's a 'twin' room you want, not a 'double'!