When we first arrived in Adelaide we stayed at the Oaks Plaza Pier for 3 wks, in a 2-bed apt for just over $210/night. Its a great place; very hotel-like with good restaurants if you don't fancy cooking, and right on the beach. The drawback is that the car-park is an additional $18/day for a multi-entry pass, although you can take a chance & park just up the road in the (free) car-park of a nearby hotel. The risk is that they may not look kindly at you, but I knew of several of the Oaks staff who parked there!
We stayed in Quest Apartments in Melbourne. They're a franchise, so the exact level of quality can vary and we haven't stayed with them in Adelaide, but we were in two different places in Melbourne for a total of over six months. Nothing special, but they did the job & felt almost like a home.