A.E. Rarely if ever would one say:
exchange s.t. against s.t.
exchange s.t. for s.t.
However, with the compound noun exchange rate it's correct and common to say:
The current exchange rate of the dollar against the euro is low, high, favorable, f**ked or whatever it is at the moment.
As for the original help request,
It's all about context, @RES-can. But yes, in these times, particularly, every ad you hear in the US is: Need some cash fast? Cash this, cash that.. so yes, it has been overworked in schlocky advertising.
Sadly, it is what far too many people need immediately... But to the point:
Imagine I were outside my home talking to the guy I pay to do my yard work (= gardening) and I needed someone to spruce up my garage door. It would be a very normal, friendly and engaging way to ask...
Want to make a little extra money for your time?
... for a few hours work?
Care to make some cash for a bit your time?
Want to make a few (extra) bucks? I've got a little job for you if you want it... pause for reply
I'll (gladly) trade you some (extra) cash for a bit (more) of your time... pause to let the temptation sink in (Would you) Care to (or just: Wanna)... paint my garage door (for me)? ...bang my fat cow?, etc..
'for me' is grammatically superfluous, but not psychologically. It can butter on a bit more sense of personal indebtedness and also helps to smooth out any abruptness in a request.
Dough is perfectly alright, but a few might find it slightly quaint. Cash seems to always be in style ;-)