If you want to solve as commercial math or accounting point of view. If accounting point of view I will find the total difference and suggest which plan to accept.

Alternative method1.

Were the fixed cost comes around $9400 which includes  depreciation and yearly contract fees. The hourly rate is $15 per hour. Total hours per year will be 40 hours per week X 52 Weeks = 2080 hours.

Alternative 2.

The average fixed cost is equal to $6640 (interest and insurance) and increases each year slightly due to compound interest rate.

Computer service fee is $24 per hours.

May be you have to use variance analysis which I did long time ago and can't remember how I did.

From accountig point of view plan a is acceptable.