Anything else is as good as a Hot S, they are the worst tyres known to man. The only people who use them are tarts who want the tyres to match the colour of the rest of their bike...
Anyway:
Maybe something like a Fire XC on the front. I think they're under 500g (especially the 1.8), and they're good tyres, not too expensive. For the back, 900g limits you. Don't you know that weight saving is soooo last millenium? If you really need to get below 900g, maybe try something like a Panaracer Megablaster. They are (/were?) dirt cheap and about 860g I think. Check the component weights thread in the FAQ.
Or just jump on the Maxxis bandwagon and get a 2.35 dual ply 40a (1300g ish).