It all depends!
Re bank costs
How many transactions, how much turn over; how is money coming in (cash; bacs; online portals; or cheques?)
If it is a small business then charges should not be too much. I pay about £5 per month but all my in and outs are through auto transfers.
Re Accountant costs?
Do you need an accountant at this stage? Arrange an interview with a few as they will give you an hour or so free and tell you what to record and how. I only pay mine once a year to do the accounts. It will vary upon whether or not you are a limited company and if you are asking the accountant to do other things such as VAT returns, employee returns and tax, and pensions.
If you will be paying yourselves a salary out of a limited company you will have to notify HMRC in real time of each payment,
If at the moment it is just you and your colleague, you will have to pay into a pension, but need not register for VAT until you reach the threshold if you are supplying in the UK ( digital sales abroad are more complicated)