Well it can be an expensive hobby.  It depends a bit on yourself really. I've seen a dinner service that sets you back as much as a real one. They are beautiful though.

But I bought some good joblots of dolls house furniture and have been lucky with bidding on some other little stuff. I'm going to try to make my own dolls with fimo clay and also food stuff. I'll be making my own curtains and will be making wooden flooring out of lolly sticks and varnish those. There is a lot you can make yourself if you are a bit handy and artistic.

You can also paint the furniture yourself and make it more expensive looking if you like. Maybe in an oriental style or a bit French with lots of white and gold. 

I like to keep mine as much as possible in the Victorian style..,so you won't find a vacuum cleaner or a fridge freezer in my dolls house...hahaha. Of course there will be some stuff that is not totally correct, but that is allowed in my book. Also the scale of things doesn't always pan out very good, but at the end of the day it has to be fun.