Marshalls, TJ Maxx, etc. and get some cheap Samsonite or American Tourister type. It doesn't really matter.
If you travel more often (at least monthly), then spend the money on a more expensive (and durable) brand like Briggs & Riley or Tumi.
TravelPro is a good in-between. Less than half the cost of a $600 Tumi bag, but good warranty and still durable.