Perhaps this question could be re-interpreted like this...
Does it have to be money that is exchanged in showbiz? Why not admiration, social status, reputation... all those intangible, but real, items of value. So even in a non-commercial setting or everyday life one could still be "performing" for some sort of brownie points.
I still tend to think this stretches the term showbiz beyond being meaningful though. It's fine to make an analogy or comparision, that informal singing could be "like showbiz", but I tend to think you have to "be in the business" to qualify as a real "showbiz performer".
And isn't "showbiz" a bit antiquated anyway - like Barnham and Bailey Circus era stuff?