Complex sentence: The Xylobands, which concertgoers were allowed to keep after the show, were costing the band approximately €490,000 per concert, eating up most of the profit from each show and thereby causing them to wonder if they would be able to continue giving them out.
Split into simpler sentences: The Xylobands, which concertgoers were allowed to keep after the show, were costing the band approximately €490,000 per concert. This ate up most of the profit from each show and caused the band to wonder if they would be able to continue giving them out.