Yeah, the briefcase of cash is supposed to reflect on the monetary reward but the UI doesn't really work well for that. We're planning to change part of the UI to better accommodate rewards that come in items (like the briefcases), but that might come a bit later in time as our UI artist has a lot of work lined up for them at the moment!
For the cash reward itself though, this might be a genuine bug, I thought the briefcases sold for 75k each? If it's selling for 50k I'll have to clarify it with Chris whether the briefcase rewards were changed or affected by difficulty