If they are non-power seats, I believe it is much easier than if they are powered. Megan's 4Runner has powered seats and once you remove them from the vehicle, they are stuck where you removed them. My truck was all manual, so I could move them around when they were out.
If the Kia is anywhere as easy as my truck, it'd be worth it, but her kia would be down for a while during the process.
I didn't get these priced at any other place, but I'd say it'd be a couple hundred dollars minimum. It might be worth it to someone, but not me!
I didn't mention that these seat heaters were trimable (I think!), but I didn't trim them down. That might make them easier to slip in. Also, heads up on the passenger seat- they have air bag weight sensors so make sure there are no conflicts. My truck had an air cushion with a tub running to a sensor under the seat. Megan's had electronic sensors right on top of the pad.