Go to the pawn shop or used sporting goods store and buy a pair of roller blades for $10. Unbolt the 8 wheels, and throw away the rest. You're good for life.
I just went to the sporting goods place and bought the $1 wheels that weren't cool anymore. A small tube with 10 bearings is about $10. Make sure you get the crush sleeve that fits between the bearings, inside the wheel.
As posted above, some spray cleaner and then a few drops of teflon lubricant will freshen up your noisy bearings, but new bearings are cheaper than buying those products (if you don't already have them).