I have a 2003 IS300 which I love. It is a fun car to drive, and incredibly reliable. However, there are a few things I do not like, and they may relate to your questions.
I have the 5 speed manual transmission, and in my opinion it's a really lousy transmission and clutch. I've driven manual transmission small cars since the late 1970s, and this one is by far the worst shifting one I've owned - very difficult to shift smoothly, and the shifter itself feels sloppy. My impression is that Lexus offered a manual transmission in the IS300 as an afterthought, and didn't really do a "Lexus quality" job with the design. However, aside from not liking the way it shifts, I have had no trouble with the transmission. (I complained about this when I bought the car new, and the dealer let me drive a couple of other new ones to show that they're all the same way.)
I think you really need to watch out in terms of snow and ice, although I can't say how it is with snow tires. My car is TERRIBLE in any wet or slippery weather. It is by far the worst car I've ever had in that area - very difficult to even drive in rainy conditions without tire slip. I have to suspect that it's partly due to the sport tires you have to use on this car - but I'm on my 4th set of tires now, each one a different brand, and it's had wet weather traction problems with all of them. In my opinion, you'd be happier with either front wheel drive or all wheel drive in that respect.
As to repair costs, it's hard to say since the car never breaks!!