Trans fluid $$$???

I found bungs cheap for a 1/4" pipe plug, and I weld them in myself.
I've used 1/2" fine thread nuts and short stubby bolts before too, a gasket/washer for a 1/2" oil pan drain plug is the same size and common as dirt... Cheaper and just as good as buying a pan that comes with one.
Unless that is, yours is bashed or rotted and needs replaced anyway. Oxy acetylene and a coat hanger or flux coated brazing rod works good for attaching the nut to the pan if you don't have a MIG