If you were going to fill the details in yourself you might as well buy a stamp and send it in yourself rather than pay $250 for the accountant to do it.
I'd do it myself, it's not that difficult to estimate what taxable income you should be paying PAYG tax on, the rest is just filling in the form and sending it in. The only thing that would make me want to do this through an accountant would be if I was unable to determine an estimated taxable income for the financial year which would be dependent on the complexity of your investments.