Flight or Bus.. There is a direct bus that goes to Leh from Delhi but it operates in summers(June to September) only, you may also take the HPTDC delux bus that leaves from Manali but even this service is there only for Two months mid July to mid September. In case you are visiting in winters then flight is the only option.
The fare for the bus from Delhi to Leh is around 1400, the bus takes a night halt at Keylong, follow this link http://vargiskhan.com/log/delhi-to-leh-bus-service-fare-schedule-book/. , http://vargiskhan.com/log/manali-to-leh-bus-service-frequency-fare-book/ ..these 2 article would help you. my advice is to take the HPTDC bus,
Hey Nikhil, Routes to reach Leh from Delhi 1) From May to October you can go via road to Leh through Manali or Srinagar 3)In rest of the months road remains blocked due to snowfall so only option is via air Option via road : 1)Bike 2)Sharing jeeps from Manali to Leh
3)Private cabs from Manali
4) Bus from Manali to Leh Hope this would help you.
The two best routes to take from Delhi are either the Manali route or the Srinagar route. You can drive down to Manali from Delhi or take a flight, the same goes for Srinagar. Along the way to Ladakh, you can make a few stops at popular tourist destinations. You can at Sarchu, Shargol, Drass or Kargil.