The YAS 26 is available on places like craigslist anywhere from $400.00 to over a Thousand! They are more expensive, as you might be aware, if you buy a new one! If I were you, I'd give the teacher of that beginning class you were in a call. Ask him (or her) about what to get? The Yamaha would be my personal choice since I own a Yamaha tenor. I have had no experience with the Jupitor.

Check the Serial number on Jupiter if 2006 and newer is what you want. But play or take someone with you and play it. If the serial # dates before 2001 avoid it. From 2001 to somewhere 2005 they became better but I think late 2005 they started making on better machining tools. Yamaha is great but PLAY THE HORN only way to tell is to play it. Keep in mind as you get better try new mouthpieces it can make a night and day difference in sound.
I have an old Martin student sax with a meyer mouthpiece and it now sounds like a pro model and I get compliments on the sound all the time. Tried the same mouthpiece on other student grade models and did great on an old mexican conn alto and terrible on Selmer Bundy. So great deals are out there google away the exact model you are interested in and do your homework. But how it plays, feels and sound are the main issue. As to repairs on vintage horns usually its a one time deal repadding and such as long as you take care of it. I don't care about looks I'm all about the sound and action.