Well for 280 you could buy a rebuild kit for the 15x,xxx and still be a under 550 but then you have to rebuild it, or pay someone to do it. There are alot of presses and stuff required to do it yourself and a shop would probalby charge around $400 for parts and labor to do it. something to think about
680ish for a rebuilt tranny
550 for one thats most likely good but you never know
280 for one that is a gamble, could be good could have shot syncros