Hi EFers,
I just saw this thread - great idea!!!
If a dinner thing is a bit much for everyone, why not scale it down to two courses instead of four - Dessert and cocktails
People could have their dinner at home or those who wanted to eat out could organize to book a restaurant that suits their budget.
The evening could start at 20:00 hrs and be more a chocolate, strawberries (June is the season!!) and champagne cocktails event. Perhaps a dance floor and some appropriate music might work, too?
I have just noted this down very hastily without checking out prices, but perhaps a buffet dessert, champers and venue could be done for 50CHF a head? For those who wanted more 'drinkies' I'm sure there are some nice venues in a nice location that have someone on the bar.
To make it a bit more Swiss, you could, for example, support a mountain restaurant venue. Those little chalets are the perfect size for 50 people and they have stunning views

.
I'm a crappy organizer (couldn't manage a pi$$ up in a brewery

) but perhaps it's a spring board for the OP?

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Have fun,
Puddy