Rent and other necessities will be much cheaper than Shanghai (about a half hour--one stop--by train) and a little cheaper than Suzhou (one stop on the same line in the other direction.) A fairly newly redecorated one BR apt in the middle of town will probably go for 1000-1500, maybe less if you look around, and a nice 2 BR will be about 2000Y a month.
Wages will be in the 5,000-6,000Y range for a learning center.

Just over a year ago I spent about a month of teaching there, no contract. (It was offered every few days but never materialized in form.) There is a large contingency of Taiwanese business people there, which I would guess to be the majority of your student population. Little language centers--consisting of only one or two teachers, and a Taiwanese manager--pop up like mushrooms constantly. The one I was interred with had a Taiwanese manipulative freak show of a woman that was on her 4th attempt to run a language center in China in five years. She was clueless at being a teacher and clueless at being a business woman. During her little attempt that time, I was her second teacher in five weeks (the other pretended to be sick and fled) and she was already on her second, then third office assistant. She lost the classroom space that she had rented by not keeping up wth the rent (but she went out for massage, drinks and swims almost every night and had some of the fanciest nails I've ever seen, courtesy of the nail salon across the street) so she was starting to convert the shared apt into a classroom.
But this is just one review about one place, so don't base your decision on this. But I would be rather careful about hiring on to a company run by Taiwanese in China, only because of the built-in political problems between them.

Kunshan is a pleasent city of about a half million, considered to be a part of Suzhou actually. For things to do there is a rather nice and uncrowded park in the middle of town, one or two streets of shopping, and the usual restaurants. (The Ming Tien restaurant at the end of TingLin st near where it meets RenMin st serves a very acceptable plate of speghetti!) But thats about it. I would guess you would find yourself taking day trips to Shanghai or Suzhou A LOT if you took a job there. (And native Suzhouites look down on Kunshan as if its a retarded step sister.)

Good luck with your decision!