+1 Always replace the bearings with loose ball bearings. You are that far into the bike, why not do a complete job. I pay about 2 cents each for 1/4 inch loose ball bearings, so it costs me 44 cents to replace them, plus a couple of cents worth of grease.
Net, open up the hubs and get ready to replace them as well. If you continue to ride the bike without servicing the bearings, you run the risk of damaging cups and cones, which will be a pretty big hassle, and cost a lot more than the cheap ball bearings.
Any bike shop will gladly sell you ball bearings (marked up of course, they have a shop to pay for).