Cathus, I had some suggestions, but I think you've covered them all!
I regularly do inside shots, and I do buy stuff to photograph. I trawl charity and junk shops, in the hope to find cheap and interesting/good looking/odd/different things that I think will make a good photograph.
It does cost money, but never more than a couple of pounds. The most money I paid recently, was £4.99 for a steam thingy. Don't know what it is yet, probably an argricultural track engine, but it does not really matter, as I like the end product.
Here's the end product:
