Amazon UK offers the Big Hero 6 on 3D Blu-ray / Blu-ray for $6.57 (£4.99). In-cart, it drops to $5.47 (£4.16). With $4.05 (£3.18) for shipping, that's $14 under the price of the regular Blu-ray version elsewhere.
Note: Although the movie will play on US Blu-ray players, the extras and special features may not. It is temporarily out of stock but can still be ordered at this price and shipped when available.