Bargain on
Definition 1 of 1
Pro Tip 1/3Expectation Clash
Use 'bargain on' when you expect one outcome but face another, often causing surprise or adjustment. 
She bargained on a quiet evening, but the party next door changed that.
Pro Tip 2/3Plan Disruption
'Bargain on' can indicate a situation where your plans are interrupted by an unexpected event. 
They bargained on sunny weather, yet it rained all week.
Pro Tip 3/3Hindsight Emphasis
'Bargain on' is often used retrospectively to express that an event was not anticipated. 
I had bargained on a small gathering, not a full-blown surprise party.