With subsidy, you already are paying your phone's cost for two years in the plan, around $25/mo extra, compared to a plan without the subsidy. That's $600 in two years you will have to pay for the phone in addition to whatever you paid. So, if your M9 was originally $200, you end up have to pay $800 total.
I personally no longer pay for such stupid subsidy. I buy phones that was a year old model. For example, my M9 is $250 bought without contract new from BB (eBay also is a great place) and use with a non-subsidized plan that's $25 cheaper each month that my original subsidized plan. Next year, I will switch over to M10 if I like or any other phones (no more than $300) while you are still paying for your original M9