If you are flying with someone because you invited them along for the experience of of a ride then it is taking the p1ss to ask them for money unless they have approached you for the ride. The Chef/Ferrari analogy made me smile I have to say
One thing I have found out is that taking someone up for the company and experience and not charging them can pay dividends in other ways at a future date that far outway the £50 I would have got !!!!
If you and a group of mates need to get somewhere and you are flying then by all means split the costs! A mate of mine does this each year to get him and his mates to Le Mans for the racing.