Complex sentence: Checker could not hope to compete on price, which thanks to inflation sent its cars soaring to almost $5000 by the middle of the decade, which was Buick or Chrysler territory and a large sum for a dated car with unimpressive build quality.
Split into simpler sentences: Checker could not hope to compete on price, which due to inflation had risen to almost $5000 by the middle of the decade. This was Buick and Chrysler territory, and a large sum for a dated car with unimpressive build quality.