knowlesy
Well the most important thing is that you are going to Le Mans, the greatest race in the world.
Cost: probably cheaper than going to the British GP. Depending on how you go, where you stay etc. £200-£300ish.
Page & Moy style with qualifying: Don't think so, all the tours tend to be for the race only. Having done this for 3 years, I wouldn't recommend it for anything other than the absolute minimum. Going overnight Friday means you are knackered before the race even begins.
Where is it best to order tickets: Someone else can hopefully help with this, I camp at Arnage where you can just pull up and get a permit.
Another option is to talk to people here or in other forums and join a regular group going down, saves a lot of hassle the first time. If you want to leave it late, there are always people selling tickets and needing people to join groups in the weeks leading up to the race. I think ferry crossings book up early though - again others will be able to better advise you on that.
And however much planning you do, you will be packing the car at the last moment, forget your suncream and have the best weekend ever!
See you there