yes they all mean except....
However, hors is more used in literate, which mean you don't speak French with this word. You only write with this word. But we use hors de to express "outside / of out of"
Sauf can also mean but and apart(apart=except, technically) , for example,
Ils avaitent totes les tailles fauf la mienne
(They had every size but/ except mine)---It really depends on which words it sound better in the English sentance when you translate
Le film etait bien sauf la fin
(The movie was good apart/except from the ending)
En outure does not mean except. Instead, it means "In addition"
For example,
Cette machine nous permettra, en outre, de faire.
(In addition, this machine will allow us to do.)
I hope it can help you
参考资料：my grammar book and dictionary, and also my knowledage