No need to thank me. Doesn't cost me anything to tell the truth.
... unless that was a sarcastic 'thanks' in which case, uh-- insert witty reply here!
Other options:
[text]
No need to thank me.
Doesn't cost me anything to tell the truth.
[... a pause.]
... unless that was a sarcastic 'thanks' in which case, uh-- insert witty reply here!