Ditch as many of the steel parts as possible, but don't obsess about grams. On my commuter my bag daily weighs 8-10 lbs that's lbs not grams. Wheels and crank if both are steel will give the most bang for the buck if replaced. Keep your eyes open for a possible donor bike too. I picked up a 80's Raleigh mixte with all alloy stuff for $40 when I was building a bike for my daughter - then sold the cro-mo frame for $20 after I stripped it.