Living in Luxembourg is of a high standard but it is not expensive, depending on what you are comparing it to of course.
40% of the country's population are foreigners, many of which are renting thus accommodation is easily available. The biggest problem with Luxembourg is the bullsh1t, you might have to sign a 1, 2, or 3 year agreement on a property, deposit 3 months rent and all this is governed by the law of the land and, in most cases, is not negotiable. I survived 3+ years there though.
There are many standards of accommodation available, in the top notch areas or the not so top notch. If you don't mind a 30 minute drive to work you can also choose to live in Germany, Belgium or France!
To ask the price of a 3 bedroomed apartment is like asking how long is a piece of string!