I can buy UN26 Shimano cartridge bb on line for $10 here in the US. Places like Jensen and Niagara Cycle sell at that price.

My basic rule on bottom brackets, is that I rebuild the cup and spindle units, until either a cup or spindle needs to be replaced. At that point, I go with a UN26 cartridge bb. The exception is on old french or swiss threaded bbs. Thats a whole different topic.

Sounds like you are reusing loose ball bearings (bad idea) and got the count wrong. Balls just do not randomly escape.

Loose ball bearings cost about 5 cents each. Reusing old ones is false economy in my book. It takes a microscope to really see wear/defects in old bearings (unless they are obviously toast). Myself, I do not own a microscope, so I just replace them.

If you are going to continue to use spindle and cup bb, spend some time reading up on how to properly install and adjust them. You should not be having problems this quick.

Once you read up on the adjustment process, you may just decide to go with a cartridge bb instead, as its just install and go. Of course, you will need the right size, and a couple of tools.