Waiting a few months after a show has come out on BD or DVD tends to help with pricing, as prices are often much closer to MSRP on release than afterwards.
Perfect example was a number of shows on WB / Fox that were last season's season sets of a number of shows, which were:
Vampire Diaries S1 - $27.49
Fringe S2 - $27.99
Supernatural S5 - $25.99
Smallville S9 - $27.49
Pretty close to release, they were $44.99 - $46.99. Their current prices on Amazon on BD are listed above. All of the above on DVD are $19.99 right now and were between $27 - $35 close to release.
If you go to camelcamelcamel.com, you can look up pricing on Amazon for any item where it will show pricing history for Amazon's prices, third party prices and used prices. It'll give you some idea of how the pricing for those items can go.