Whilst not directly answering the question, I find as an accountant to SMEs the best place to start is to arrange a complimentary meeting with a good accountant to discuss your new business idea, go over what it is you want to do, your goals for the business, discuss the business structure options (such as a partnership, trading company or trading trust) as there are advantages and disadvantages to all structure options. The structure you go with will have a direct impact into accounting costs etc. Please note I did not mention Sole Trader as I presumed there would be at least two of you involved in the new business.

At the same time should discuss things like turnover and requirements for BAS, number of planned employees at the start and over the next 12 months as these will determine which would be the best cloud based accounting software for you. I have had some clients start up a new business to see if grow so fast that they started with two employees (themselves) to employing over 10 staff members within the first 6 months meaning the payroll admin side of the business exploded and accounting fees also went up. There are numerous options out there like Xero, Quickbooks and MYOB just to name a few. Again the costs here do vary and will impact on costs. You should also discuss your experiences, if any, running a small or start up business, as well as the experience you have in the industry you plan to operate your new business in. This will help your prospective accountant to garner an idea of what level of input and support you will need and the costs likely to be involved is his or her services.

Basically, the greater the picture you can paint of your business now and over the next 2 or 5 years will help at your meeting to review what will be required of your accountant and costs accordingly. On a broad level view, fees to do what has been listed above for a company structure and the personal returns for the two directors / shareholders have been as low as $1,500 and have gone up to over $10,000 for some clients. Abviously the higher costs involved significantly more input and touch points involving more advisory work rather than the complaince bookkeeping work
 

Ideally your accountant should have a good ballpark for pricing on their website.
If your business is doing around 50 transactions per month, I'd allow (per 2020 pricing):

• Tax Compliance - Tax Return / BAS / Annual ASIC return / tax planning - $200+GST/month
• Bookkeeping on a monthly basis - $200+GST/month
• Payroll - 2 employees - $50+GST/month

We would make software suggestions for free but allow $250+GST for a basic setup of Xero (for a new business).
& $1,000+GST for the company setup (inc registrations, documentation & associated advice).

For more details on pricing just check out:
https://www.fullstack.com.au/pricing/