The best substitute I could find is Fishpond. They are apparently Australian in some way, their prices are in AUD and for orders over $50 they ship free.
However, their prices are inconsistent - and have changed with some books drastically. For example, The Testimony of the Beloved Disciple when from $35 to like $60 something. However, they are probably the cheapest place I can find for N.T. Wright's Christian Origins and the Question of God series.
- The New Testament and the People of God (Vol 1)
- Fishpond: $40.68 | Koorong: $89.95
- Jesus and the Victory of God (Vol 2)
- Fishpond: $42.98 | Koorong: $82.95
- Resurrection of the Son of God (vol 3)
- Fishpond: $47.27 | Koorong: $99.95