Walmart offers Person of Interest on Blu-ray Season 1, Season 2, or Season 3 for $12.96. Opt for in-store pickup to avoid the $5.99 shipping fee. (You can also spend $35 or more to qualify for free shipping.) That's the lowest price we could find for any of these seasons by at least $8, outside the below offer.
Also available is Person of Interest on Blu-ray / Digital HD Season 4 or Season 5 for $12.96 via in-store pickup. (Amazon has the fifth season for the same price.) That's the best deal we could find by at least $5, outside the below offer.
A close price: ImportCDs via Rakuten offers the first four seasons, with prices starting at $10.56 plus $2.98 for shipping.