http://users.cooptel.net/ianwatson/nwptuf/MfR_808_A.pdf This website says it'll cost £5.95. It doesn't say if that's for a single or a return. It takes over two hours though. Might be quicker to get a train. That costs about £9.00 with a railcard.

If its the ARRIVA one with no Under 16 card it'll be a £6 return (Arriva Day Ticket - valid on ARRIVA buses on the route only). If your under 14 you ecan get a £4.50 one though. I'm not too sure on the Stagecoach in Cumbria workings - the only fare i know of theres is the £9.50 North-West Explorer, but im sure thats not the cheapest option!

The only service I can think of from Edinburgh to Carlisle is First Edinburgh service 95. From memory, the through service is about every two hours. Phone First Edinburgh at Falkirk for the fare. (It's not cheap) From Carlisle to Windermere, you would take Stagecoach Lancashire service 555/556. You might have to change vehicles at Keswick. Phone Stagecoach at either Keswick or Preston for the fare. Bus fares are not generally available on any website