Heh, no I excluded that!
Accommodation: 4 nights at $50 in the US = £105, 4 nights at £30 in the UK = £120
Badge: $70 in the US = £37, £75 (very early bird, with tickets) in the UK
Tickets (assuming playing every session): $33 = £17, £9 in the UK, I think
Total: £159 in the US, £204 in the UK. That's for a single dorm room in the UK (shared bathrooms) vs three sharing a hotel room with one bathroom in the US.
Of course, the convention in Indy is always going to be streets ahead of the UK one - the scale is incomparable. Nevertheless, you'll not spend /that/ much more money on GenCon UK, and considering the cost of land and living here compared with the mid-west of the US, it's not surprising it costs more!