Automatic transmission swaps?

[Pbmattc]

I have a 1989 nissan 240sx engine type KA24E. I have lost third gear, i have removed the transmission, and found that a rebuilt or new transmission cost around $1,100. I have noticed that the bell houseing and main transmission body appear to be able to be seperated. My question is are their other automatic transmissions that will fit this engine or my bell housing that are readly available and cost less?