if your going to get a second hander i was told by the tranny guy i use (been at it for 35 years) get the torque converter and trans from the same car. if you use the TC out of the shagged trans, all the debris and bad stuff will circulate back through the replacement trans and burn it out all over again. i took his word for it....
i got the trans rebuilt in my vp and decided on a reconditioned TC. peace of mind that im not going to run a bunch of crap through my brand new box.
i paid 600 for the box rebuild and 200 for the change over TC (all cash). i supplied a transmission from the wreckers (he didnt have one on the shelf), then when it was ready did the extract and install in one afternoon.