I used to do my own payroll using Excel spreadsheets that I built myself, filed all my own tax returns, etc... I would periodically double-check my calculations by using Quickbooks free pay-check calculator, here: https://quickbooks.intuit.com/r/paycheck-calculator/
Now we are using PayChex. For up to 5 payees, we are paying $28 per weekly payroll period (which includes their tax filing and payment service, and direct deposit for our employee's pay checks), but that is a discounted rate worked out by their local sales rep.
Since we are a seasonal business, we don't pay anything when we don't have a payroll to process -- just a $100 dormancy fee.
Square's payroll service is not available in all states, yet.