Summary of expenses:
1. Accommodation at Balmer's: 30 euros/personight
2. Train ticket to Lauterbrunnen: 15 euros/person
3. Reservation fare from Paris to Interlaken: 44/person.
4. Ticket to Jungfrauch from Interlaken: 140 euros(we didn't go)
5. Ticket price to Mount Titlis (didn't go) : 72 euros
6. Simple one-time meal per person : 7-9 euros/15-20 euros(Indian meal)
Other useful tips:
1. Switzerland is a costly place so plan your expenses accordingly.
2. Book hostels well in advance to save costs.Also, the hostels tend to get filled up quickly at the end. Switzerland is quite a popular place after all
3. Do go for the Golden Pass Train Journey.It is free for Euro Rail Pass Holders.Same goes for the train to Lauterbrunnen.
4. Same things especially apparel items are available at much cheaper prices in the supermarkets than in the streets. So buy from the supermarkets.
5. Do visit Grindelwald(near Interlaken) as well if you have an extra day. Bern can be avoided.