Some examples of DVD cases utilized for CDR releases...
Many times CDR's are released in DVD cases, typically the slim variety. Simple and cost effective.
Here's a couple examples.
Bologna Violenta – 'Il Nuovissimo Mondo' (2011)
Released by Placenta Recordings from Detroit
AODL / Vasectomy Party – 'Salt Lake / Sun Coast' (2015)
Released by Forever Escaping Boredom Records - Florida