Amazon US currently has season 3 on blu-ray for $9.99 each as part of their Black Friday deals. Even with shipping I think that's a good deal. Next best is £17.89.
Unlike Amazon UK this Black Friday deal should last a little longer than a few seconds.
First post hopefully everything is in place.
Thanks to fleetingmind for pointing out that seasons 1 & 2 are available at the same price.