I did a trip to the Geneva motorshow this year. Different from the sort of show you're talking about but worth thinking about.
I paid for a trip for a Christmas present for my dad. Flights from Bristol were about £140 return for the 2 of us, arriving about 1pm and leaving at the same sort of time the next day. The expo is pretty much on the airport so you can jump off the plane and straight into the show. Tickets for the show are only about £15 each although you can only go in once so if you want to go back the next day then you need to buy more - but they were readily available from booths outside with no queues.
The show itself was excellent - absolutely HUGE. Pretty much every manufacturer you've ever heard of there and some you haven't. It wasn't too crowded and most of the "normal" stuff you're free to get into and have a poke around. The exotic/expensive stuff is behind barriers and presumably if you can prove you earn enough they let you in. But you get close enough to have a proper look and take some good photos. The beauty of it is that Switzerland doesn't have a car industry so it's properly impartial and independent - imagine if this was Munich, you'd have all the German cars in the best booths at the front of the hall.
We had originally planned to stay till closing (about 8) then find something else to do the next morning but by 6 o'clock we had only seen about half of it so decided to go for an evening meal and come back the next day. We got a hotel near the airport, Geneva public transport is super efficient and you get free tickets as a tourist. Geneva is EXPENSIVE though so prepare to bend over for accommodation, meals and drinks. 2 cans of Coke at the show were about £9, 2 ibis budget hotel rooms came to nearly £400, a pint of beer about £7 and a meal for 2 (a pizza and a beer each) was about £60. It's a nice place, I work there regularly so know it well - always found it a bit clinical for my liking but it's a pleasant place to spend an evening. If you're geeky then CERN have a little visitor centre at the ATLAS experiment on the LHC and it's easily accessible on the tram.
So £500-£600 for a good motoring based break in an interesting city, I'd really reccomend it. Although our flight home was so badly delayed that I got €500 compensation which nearly paid for the trip
