For the trip down south.. Just an idear came into my head about accomidation.. depends how far down south you wanna go...
I have a very good friend who lives on nanarup beach 20 min out of albany. Hes got a massive property and i'd have to ask but hes like a father to me and loves to party so i doubt the awnser will be no.. but depending on numbers.. bring a tent.. and camp the night.
Otherwise.. There are heaps of places down that way to stay.. Troy and i stayed in a on site van when we went to albany.. $30/night.
Its a beautiful drive though margret river, pemberton, and that way.