Amazon UK offers Titanic Collector's Edition on Blu-ray 3D / Blu-ray for $7.66 (£6.28). Add it to your cart, and it falls to $6.38 (£5.23). With $3.76 (£3.08) for shipping, that's the lowest total price we could find by $23. It includes both 2D and 3D versions.
This Blu-ray is region-free; the film will play on U.S. Blu-ray players, but the extras and special features may not.