From Shillong Cherrapunji is 1 hour away, while Dawki is 2 hours away. Same way east Khasi hills are 1 hour away and west Khasi hills are 2 hours away. So my suggestion would be you staying in Shillong from where you could cover all these places at a minimal distance. For cabs kindly check with MMT and savaari.com. Goibibo too supplies cabs on rental basis.