Hi m8...
I also look for something like that myself.
Check this list:
http://en.wikipedia.org/wiki/Free_audio_software
Qtractor seems like a nice Cubase alternative but I haven't tried it myself yet due to lack of time.
Audacity is pretty good if you just want to edit your tracks and add effects. It's an alternative to Audition, Sounforge etc.
Not sure about their plugin support but I look into it. I ll post back if I find anything.
Of course you can get an older version of Cubase for far less money. I think Cubase SX 3 costs about 120Euros at this time. And for home projects you don't need 4.
But what kind of music do u want to create? You want just a mixer/editor? Do you plan to use MIDI?
Cheers!