Well, my first question is where do you live??
If you are in cold country and you wait 'til Christmas, it might be sitting in your garage until next spring!
I'd probably get the bike I can afford and ride it while saving for the 29er... and in the Fishers you get A LOT more bang for the buck in the standard size bike... I bet the componentry on the Piranha is virtually identical to that of the Cobia (with exception of the 29er fork of course)... So is it worth twice as much just to have 29" wheels?
I was in a similar situation when I bought mine and I also had my eyes on the Cobia. But I got soooo much more bike in the Tassajara Disc for less money, that I went that route. I am going to get a 29er eventually, but I am now leaning towards giving a Redline Monocog Single Speed 29er a shot... (I can get it locally for around $400!)
You can always sell the Piranaha when you have the money for a Cobia (or any other 29er..). Take good care of the bike, keep it well maintained and clean, and you should be able to recoup a decent amount of the purchase price on ebay. Newer Fishers seem to do very well there.
