Well, Ian, I've played a few of the light weight 88s (M-Audio, Studiologic, etc.) and the code word to watch out for is 'semi-weighted'.

None of these so-called lightweight controllers have anything in the way of an action any closer to a real wooden action as a G70 (or PSR!). OK, they get the SHAPE right, but that's about it... If the actual FEEL of the keyboard is of any importance in an 88, I fear you will have a long wait for anything that FEELS like a piano to get under 25 lb.

Best of luck, though. Let me know if you find anything close at 25 lb. Could use one in the home studio (just got K2500 and Roland 76's at the moment)...