My husband and I will be staying in Murren for 8 days (later this month). We will be hiking, and probably traveling from Murren to Lauterbrunnen, Wengen, Kleine Scheidegg other places on both sides of the valley during our trip. We may take a day trip to Bern. We've already purchased Swiss Half-Fare Cards. These provide the same 50% discount to the Schitlhorn and the Jungfraujoch as the BO pass. So the BO pass gives us no benefit there. Will we really rack up more than CHF 250 (the cost for each of us for an 8-day BO pass) traveling around the Berner Oberland using our half-fare cards?
Only you know how much you will use the trains/cables but you have to look at it from 2 perspectives - cost, as well as convenience. When you have a pass you just walk on/off whatever trains/cable cars in the validity zone you want to use without ever having to buy a ticket. It means you don't need to pre-plan and if you suddenly change your mind and want to go see something different or add on something you weren't planning, you just go. To me that has huge value. It also means you end up seeing/doing things you might not have otherwise. Sort of the all-inclusive mentality. If it's included, why not go see it? Or if you particularly love something you can justify going to visit again.
We live in Murren for the summer every year and with a pass sometimes we'll just decide on a whim one afternoon to take the cable car down to Gimmelwald for an hour to go get a beer and walk around or hey, they have something down at the Lauterbrunnen Coop that they don't have at the Murren one, I'll just go run down and get it. When you have a pass, those types of trips incur no thought because they are "free". That adds another element of relaxation to your time in Murren.
I think you'll find that when all is added up you're within $75 +/- and to me the convenience factor is well worth that amount if you end up being slightly off.
I have to agree regarding the convenience factor. Plus, when you start to figure in the planning, etc. it really is so much easier to show up and go. Round trip from Lauterbrunnen to Eigergletscher is CHF42 per person. A one-way down on the cable car to Grindelwald Terminal is CHF16 each. So costs can add up quickly.
I won't to try to discourage you or encourage you either way but I will suggest that when you go to Bern and back or Lucerne and back you will use up quite a lot of fare even at half price. Both of them are covered by the BO Pass.