By buying my machine, I avoid the machine leasing costs imposed by the ISP. The isp cost will be higher to protect themselves from early termination, and it should also include a service contract which can be anywhere from $20 to $200 a month depending on the costs of the hardware.

These are all costs that you need figure into the long term operating costs. They may not matter in the first 6 months, but in the 4th six month period, or 18-24 months down the road, you may need a new machine, or repairs, and where do those costs come from?? They come from the part of your monthly fee that was earmarked for machine rental/use/repair.