I forgot the exact price but they're not expensive. I got mine from an ebay seller in China and Hong Kong. Just ebay for "m42 to EOS adapter". Buy from those with 100% ratings and request if they could ship via EMS as SAL is too long but I got mine via SAL but never again!
Here's my test shot from the Helios 44-2 before I sold it to Aris T_T. Sharp at f2 already. But women will hate you when you take a photo of them with this lens (check out my wife's photo below).
Helios 44-2 58mm f2 - a set on Flickr
Why o why did I sell that T_T