[Amazon US] The Perfect Insider Blu-ray ($18.31, via third-party seller $16.99 $17.15) - Beats Sentai's current price of $21. Historical low, from what I can tell. It's been incrementally dropping price in small amounts for about a week now.

[edit] $16.17. It keeps dropping. If you're interested, don't wait too long to pull the trigger. When it drops in small amounts like this, one purchase can shoot it right back up.

[edit] $17.15 now. Looks like somebody bit.