When checking your math you can not simply assume that there are always 4 of any given days in every month. For example, there are not four Mondays every month.
The correct method:
1 staff X $17hour x 8 hours day 5 days a week x 52.1428 weeks a year ÷ 12 months. =$2,954.75
The incorrect method:
1 staff X $17hour x 8 hours day 5 days a week x 4 weeks a month
=$2,720
Want proof? 7 days a week x 4 weeks a month x 12 months does not add up to 365 days.
365 days per year
52.1428 Weeks per year