Be careful going second hand. A neglected commercial machine can be expensive to repair, unreliable when you need it most and it's hard to tell from the outside just how much scale has built up inside. A much less riskier proposition for commercial enterprises where capital is tight is renting/leasing new equipment which comes with backup service and warranty. Without knowing exactly how busy they are going to be, and just to give you an example, if a new machine and grinder had a cash price of $6000, and they decided to rent instead, weekly payments would work out to be around $70.
On the subject of power, if you mean 10Amp rather than 15Amp, that can be done but whether a 2 group running on 10Amp is going to cater for the demand is another story. You don't want to run out of steam once word gets out about how good the coffee is!
An example of a 2 group machine that's still reasonably portable which can be configured in 10Amp or 15Amp modes which *might* be suitable depending on answers to some the questions above:
ECM Elektronika Profi Due
Happy to offer advice and/or put you in touch with someone in Brisbane,