Are you, as a non religious person, offended when people say they will 'Pray for you'?

Normally not. In most cases the intentions behind it are good. If they want to pray and that brings them some solace, I'm not gonna stop them. Though as someone who doesn't believe I personally don't think it has any effect (other than potentially soothing them) and that their time would be better spent on something else.

So long as they aren't disrespectful or condescending, and aren't trying to push an agenda, they can pray for me as much as they want; I won't get upset.

I'll usually just say "thank you" and appreciate their gesture, and leave it at that.