I’m a CPA/interim CFO and I assist over 150+ startups in SF, Chicago, & NYC with all things Accounting, Tax, Finance, & HR. A reasonable monthly cost for Accounting & HR depends on:
The volume of your transactions: do you have 300 transactions hitting your bank account and credit cards every month, or 10,000 transactions? More transactions = more time = more money.
The complexity of your transactions: even if you have relatively few transactions, they may be complex. For example, you may have prepaid Facebook $100,000 for advertising for the next year. You or your bookkeeper will then need to reconcile that account every month against what advertising amount you’ve actually used.
Doing the work yourself: if you can train yourself to do some of the bookkeeping, you can definitely save money. Two caveats though, 1) your time is truly better spent growing and managing your startup and 2) if you get it wrong it will very likely be expensive to clean up the books.
How you’ve leveraged technology: I can’t stress this enough… using technology will greatly reduce the amount of time (aka money) you have to spend on Accounting and HR. Here are my absolute essentials: QuickBooks, Zenpayroll, Zenefits, Expensify or Abacus, Bill.com, DropBox or Box, Gmail.
In sum, what you will spend on Accounting & HR for your startup depends on your unique situation.