I ride a bike and was touring in SL last Feb. I've been before and am going again next Feb.
There is a lot of accommodation in SL, but not in every small town. You may have to plan a bit. However most larger towns are not that far apart so you can normally find somewhere. The most I rode in a day was about 120 kms between Mannar and Jaffna. There's not much in between, just a few small towns, that could be called villages.
The NE coast can be a problem as it is war damaged and sparsely populated. Also, some of the resorts/hotels are military only. You just need to plan this a bit.
Have a look at crazyguyonabike website for people's tour write ups. They often list places where they found accommodation.
Tourist areas usually have a lot of competition so prices can be good. You may find non tourist areas more expensive or not such good value.
Go and enjoy.