Getting to the start of the JMT is tricky - but the first step, of course, is to get to the US. The usual airport to fly into is San Francisco, then you need a public transport miracle to get you the Yosemite in a couple of days - at the same time buying food and fuel on the way.
The arrival is complicated by the Wilderness Permit system, I applied for a Wilderness Permit for my trip 24 weeks in advance of my start date, this permit is valid for entry into the park on the specified date only - and even then you have to get there early to collect it. With this in mind I had a choice to make - arrive the minimum number of days before my start date, or build in some contingency.
In the end I settled for the minimum days itinerary, which was as follows:
This itinerary had problems - finding accommodation in SF close to the train station - recovering from 8hrs jetlag - getting about in Merced, having enough time to buy food, re-package and send on to MTR etc..
As it happened however, at the last minute a friend offered to pick me up from the airport, allow me to stay with them for a couple of days - then take me to Yosemite - how good was that? I appreciate though that this means I can't advise you about whether my plan worked, sorry about that!
I hunted about for the best deal on flights and BA seemed to be the best. I was also very impressed by the BA website which showed you a long list of flight options with the connections and total journey time clearly shown for each one. This allowed me to choose the shortest direct flight at the best price.
My JMT guidebook suggests flying in to San Francisco but back to the UK via Los Angeles, which is easier to get to from the end of the trail. The price of two flights as opposed to one 'return' flight really increased the cost somewhat - so I resolved to get back to SF from the end of the trail - thus kept the flight cost to a minimum.
One the way to the US my itinerary was:
15 hours journey time.