just for you'r information,
do you know what is 1600 pound (or euro?) for an Indian 20 day tour?
a complete rip off!
india is so cheap, people get there some 800 rupees per month of work (and even less) for 1600 euro (or around 112,000 rupees) you can basically buy a new royal enfield (the casual indian bike) and travel around 20 days with it including fuel, sleep and food!
so this is india on the other hand, tourists which are unfamiliar with the prices there are paying tons of it to greedy local tourist organizers, it is always recommended not to go to these agencies as you can do a lot on you'r own with much less money.
that's one thing,
the other is that the road to leh is not a road which a beginner rider should ride at (at least that how it was ~10 years ago), and especially not to the side valleys (as to 10 years ago again),
2nd, i wouldn't go with anyone on that road as a passenger (though the one to leh is far better than the one to Srinagar (from leh))
3rd, if you still want to do it, i'd argue the price, though if you don't mind paying so much, then just go for it and you'd have a great trip.
4th, why don't you and you'r friend, buy a motorcycle at home, ride it for a year or so (you have a lot of time till you go),
experience the ride, then after such a long period you could definitely do this trip (a friend did it on an Enfield he bought few month's earlier - first bike ever),
there are places to sleep and eat on the way, it's no issue, many stops for the trucks which goes there and tourists, no need to worry about that, also in the valleys around there should be no issue with sleeping/eating, you are not the first tourists in that region...