With the British feeling the pinch financially and selling off defence equipment, is there anything in the RAF inventory that Australia should make an offer on?
Unlikely IMO. AFAIK, the only aircraft where there is commonality between RAF and RAAF assets is within some of the lift/transport assets, things like the CH-47 Chinook, C-130 Hercules II, and C-17 Globemasters. There might be a small number of other assets where there is commonality, but those three are the major ones IIRC. And the RAAF and RAF do not operate the exact same variants, which means some form of mod work to achieve fleet commonality.
Making this more complicated is that a number of the RAF assets are being heavily utilized, to the point where if/when the assets (like the C-130J Herc II's) get retired "early" in ~2020-2022, the aircraft are likely to be shagged. Airframe age-wise, fairly young, but with a large number of flight hours on the clock.
Making it even more unlikely IMO is that the ADF as a whole is also looking at a tight budget. Not anything like the British MoD appears to be looking at, where things are being dropped or retired early, but enough so that aside from critical capabilities, new items not already planned for are very unlikely to appear.
-Cheers