yeah HMV is just crazy, i've only bought one album from them (octavarium cuz i cudn't wait for other stores to have it).
I like to get my CDs from grammaphone, sembawang (yes! they carry rock and other stuff too! not just pop!) and whenever i see discounts. like i got 3 Jamiroquai albums at 45 total =) cuz each was like 12 or so.
as for obscure stuff, try ONLINE. ship in bulk, like 10 CDs at a time perhaps. the @%*$(^ thing is that u gotta pay GST.