Well i think that it means that you loose a little and get more back...i have herad the expression loads of times and i'm told that is what it mean.You lose a shilling and find sixpence?
Is it an idiomatic expression maybe a bit outdated, or does it mean what it says?
I would see how it could mean that.I actually thought a shilling is worth more than six pence, maybe Sneaky's suggestion fits better the contest.
It's a quotation from the film Quadrophenia. The guy has just come out of a trial, he comes into the pub and the bar owner goes "Hey Jimmy,You lose a shilling and find sixpence?eh?". So maybe the intention can be something like "You are still alive after all!" or something like that. What do you think?