Usual Story... I lost my keys last night, had to stay at the hotel, and now have to get a locksmith to break into my house. I have been told that this will cost 350CHF plus tax.

Did that happen to anyone before? is that the right price?

Seems to be in the right ballpark - someone in this thread reported that she would have been charged CHF300 (fortunately for her, the neighbor's husband came home in the nick of time with a spare key.)

Unfortunately that's likely to be just the beginning, as other locks in the building will probably have to be changed and you will be billed for those as well. See this thread for discussion:
charge for lost keys