I got my original copy from ebay two years ago for 5$. It was a real headache to install it on Linux, but I managed to do it using Windows in VMware. My personal ethical statement is that you have to pay for software only if you like it. If you like some software, even if it is freeware, you can send some contribution to author voluntarily. And if you do not like some software, you mustn't pay even if it is non-free.
So I use legal copy of MM7 with runs on pirate copy of Windows which runs inside of freeware Linux which I contribute sometimes. 