Touch points like pedals, saddle, and grips are great places to start.
Good plastic and metal pedals can be had for not a lot of money (I am running DMR V6 pedals ($20) on my mountain bike, they're awesome if you're not to hard on them: the nylon pins sheer off easily when you hit rocks with them). Others such as RF Chesters can be had for a little more with replaceable metal pins and roller bearings.
After that, the sky's the limit! You may wind up spending more than the bike is worth but who cares if you like it?