My janome centre charges about AU$70 + parts for a service
I think last time I put it in on a thursday evening and got it back either the saturday or the next thursday. I work full time so getting in to the shop was harder for me.
People say you should go in yearly, but it depends on the use of your machine. Mine had never seen a service until about 18-24 months ago (my grandma gave it to me about 7 years ago and I am still learning what to do, but it does see more sewing these days than it used to).
I have a janome MC7500