Hello!
Sorry for the long delay. First, I want to thank all the people that posted here and your advices and opinions. Second, after reading the posts I decided and bought the jupiter-8, it was in an auction on german ebay, and arrived today!
I payed 30 € for the lens, I don't know if it is a fair price, a overprice or a bargain, to this kind of lens!
The industar-50 is still for sale in a similiar site, but here in portugal, by 15 euros. Other thing is, in the description of the industar the seller says "M42". I wanted a lens to my leica IIIc so m42 is a no lens! And also I thought that jupiter's and industar's were only m39 screw mount, I didn't know that they existed to the M42 cameras!
Again thank you,and after I finish the first roll I'll post here!