Garbage in, garbage out. You say you only use the lowest tier materials, so you should expect the lowest tier final product. Your customers demand low price over quality so you are meeting their needs perfectly. I think you would be shocked at the difference your printer can do with high end materials. Keep in mind that cast vinyl doesn't mean it has a high quality ink receptive layer. You will want to test many materials to find the ones that work best with your workflow, equipment and environmental conditions.
