I've gotten transmissions 'refreshed' (just new clutches with no other hard parts) for around $400 (long ago). I've got two in the garage I bought used locally and had them inspected and 'refreshed' which cost less than $500 each a couple years ago.
Last one I had 'rebuilt' (virtually all new internal parts) was about $1,650 total (circa 2017).
Last 'race ready' transmission I bought was around $2,300 without valve body. A new 'built to order' valve body will add $500.