Alowishus wrote:

I actually looked up bids on the same game on UK ebay. They were considerably less. Approx £150 - 250. Don't know if they were sealed or not.

according to professor wikipedia:

The PAL-B version of Stadium events, is common; as Nintendo never recalled the game like they did with the NTSC version of Stadium Events.[13]
A sealed copy of the PAL version is much easier to find, only 1 NTSC version is known to exist.
A boxed copy of PAL-B Stadium Events is worth under $200[13] (significantly lower then the NTSC counterpart), and a loose copy is very common ($15).
Unfortunately, Many people confuse the common boxed PAL Stadium Events, for the rare boxed NTSC version.[13] So many people in the end are losing a lot of money on a clever exploitation of the rare NTSC version.