Greetings from Melbourne South Eastern Suburb.
I reckon tennis balls are too expensive. I'm originally from Indonesia, where tennis is consider "rich people" sport and not too popular. However, the decent tennis balls such as Slazenger, Dunlop (Forte&Volley) cost roughly about $5-7 /can.
Let alone the tennis balls, Strings & tennis rackets (genuine from the authorized dealer) are also much cheaper there. For instance the Pro staff six one tour 90 cost only $170 (they might throw in free luxilon string for you if you are a good negotiator).
I just email my bro to get me Head Extreme Pro 2.0 but they only have the MP 2.0
It cost around $160-170, the same as in tennis warehouse USA.
by the way, I just bought Wilson tour tennis ball from target for about $8/can.