You can order seat heating kits for around $200 from Rostra, or one of their dealers. I installed them myself, so I'm not sure how much it would cost in labor. Also, mine was on a 2000, and I'm sure seats in a 2011 are more complicated.
I'm not sure about yours since you already have owned it, but my new 4Runner coming in this weekend is getting seat heaters added at the dealership for $400.
when i bought my 08 sport 4runner (cloth seats) i was told you can't get heated seats with cloth. not sure if it just won't come in a package or if they just can't do it with cloth.