A manual transmission lasts forever...the major wear part being the clutch disk.
A trained ape (me) can change a clutch and flex spring for around $250. I have done it many times.
Now if an automatic fails, its a little more complicated. There are dozens of friction bands, pressure ports, electronic sensors. This trained ape usually has to replace the whole thing with a rebuild. Average cost $1,200. Often more than a used engine to buy a rebuilt transmission.
I keep my cars for a loooong time. So I like to buy the manual transmissions.
I drove many convoys from Austin to Ft. Hood and never used the clutch except after a stop. I drove my dad's farm truck and seldom used the clutch, except for the first start.