Grain - There something called part gyle brewing where you use the grain a second time to make a smaller beer
http://www.thehomebrewforum.co.uk/showthread.php?t=68729&highlight=parti+gyle
Hops - I wasnt aware you could use dry hops for bittering as hophead says
Yeast- You can potentially re-use yeast infinately. There are a number of breweries that have been using the same yeast for 100 years plus. On a HB level overbuilding a starter can get you at least 13 re-uses. Some people think infinately
http://brulosophy.com/methods/yeast-harvesting/
But I think the best way to save on grains and hops is to buy in bulk. You can get a 25kg sack of base malt for as little as �ã18 and you can buy hops in up to 1kg amounts on some sites