If you are using QuickBooks payroll and paying as a contractor, they can be paid whenever and you are charged per transaction which is based on your payroll subscription plan.
Yes, there are fees associated every time you make a vendor payment inside QuickBooks Online (QBO). Let me go into detail about this.
If you're using QuickBooks Bill Pay to process these payments, you can create a certain number of transactions for each month depending on your limit. To learn more about this limit, you can contact our customer care team through the Help panel within your QBO account.
Additionally, please know that access to a limited number of free ACH payments depends on the specific plan you're using. If you want to learn more about this, I recommend reading this article: QuickBooks Bill Pay plans.