I'm wondering if you are pinching the tube between the rim and your lever while getting the tire on. Can you put the tire on without levers? Once you know the tricks, it can be done (though I always use levers to get the tire off).

Also, cheap tubes can have variance wall thickness with weak spots in some places. I have the best luck with known brands like Specialized, Michelin, Salsa and Torelli. I always seems to find something wrong with cheap tubes - weak spots, goo in the valve stem, etc.