Am planning a 10 day trip to Sri Lanka this year end (26 Dec - Jan 4).
Places I intend to visit are Anuradhapura, Dambulla, Sigiriya, Polonnaruwa, Kandy, Horton's Park, Nuwara Eliya, Galle (already booked a hostel) , Colombo (will stay in friend's place).
Would appreciate suggestions for decent budget accommodation for 1) Cultural Triangle Base 2) Hill Country Base
Try the Dambulla City Hostel for the Cultural Triangle. Very clean and cheap. For Hill Country, the only one I know of is The Kandy House, but that might not be where you want to be location-wise. Could be worth looking into, though.
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Hi' I've just got back from Sri Lanka and I don't what you budget is, but we found some decent hotels at a budget price just looking at hotels.com and booking.com.
Else have a look at http://www.hostels.com/ which seem to have a good selection of hostels. There should be plenty of options.