There's loads of motels in Dunedin, I was there for the England v Argentina game at the Rugby World Cup, we stopped at a motel called Amross Motel on George St, North Dunedin, an easy 5/10 minute walk to the Octagon (where there's a few bars) but we weren't that impressed with the place!! We had 4 in the room, so 2 ended up on a sofa bed, which was arguably the most uncomfortable thing i've lay on (having spent 7 years in the navy, I can assure you that is some mean feat ) also we had to keep asking for towels and toilet roll etc!!!! www.amrossmotel.co.nz/
There was loads of motels all along George St though, so I can't see accommodation being a problem for the lower end of the budget scale!!! I also noticed one of them Living Space places in Dunedin, it's like the halfway point between a hostel and a hotel, we stopped at the one in Invercargill for the Scotland v Georgia game and were quite impressed, good value!!! dud.livingspace.net/contact.php
Another place we considered before opting with Amross was the Dunedin Holiday Park, which is further out, on some beach, but seems to have plenty of accommodation at a reasonable price www.dunedinholidaypark.co.nz/

If anyone's going to Queenstown I can recommend 2 great places at either end of the budget scale, for a special treat one night we stopped at a place called The Rees, which is a bit out of town, towards the airport, next to a lake. We had a lake view room which was wonderful, but a bit pricey... www.therees.co.nz/
The other place we stopped in Queenstown was a motel called Amity Lodge, right in the heart of the town, was a real gem, the rooms were great and the couple who ran it were a laugh!!!! www.amitylodge.co.nz/

Sadly, it's looking likely i'll have to miss Dunedin this time, should be doing Wellington and was looking at a quick fly in and out of Auckland for the weekend but that's not looking very likely with the flights etc...

Hope this is of help!!!

4 in a room. That sound very cosy!