Everybody realizes the OP is talking about a pretty low end bike, right? Plain tubing, chrome spoke protector, brake extension levers... It's close to 30 pounds. Chances are that even if he does decide to replace the crank, he's going to use something cheap, and it's not going to be much lighter. There are quite a few modern aluminum cranks that can actually be heavier. And even if he does manage to shave a couple of hundred grams, is that really going to make it "feel like a new bike"?

I swear, some of you guys must have been beaten with cottered cranks as children.