Visa Information » Sri lanka
Nationals from Maldives and Singapore can enter visa and without an ETA. 

Everyone else can apply for an ETA. The ETA costs US$10 for SAARC countries and US$20 for everyone else. 

Sri Lankan visas can be extended for up to three months without much difficulty. 

ETA Sri Lanka 

Emabssies and Consulates, Foreign and Sri Lankan.