The official fine is 25k from you and 25k from the owner of the bike who lent it to you, totaling 50k.
If you drive by the rules, you won't be stopped.
If you are stopped - communicate friendly, don't be rude, and negotiate.
The hotel owner said to give them 1, max 2 thousand rupees. I ride my bike carefully, and we haven't been stopped even once)
But there are a lot of police officers standing around (Galle, Hikkaduwa)
We were stopped once. Everything worked.
Today we were stopped by a police officer who, due to the absence of category "A" on the international driver's license, demanded a bribe. He started with 25,000, then 10,000, and eventually 5,000. Moreover, the words that we had no money did not sway him. We spent half an hour there, and in the end, we still had to pull money out of our stash. Situations like this really spoil the impression of the island. No matter where you stop, a beggar will run up to you and start their scheme with a friendly smile.