In the long run meaning when the swap is complete the ls and automatic od is cheaper then a modern Hemi and automatic od again im talking about installing one in my car with a rms suspension where i can use a cheap off the shelf header. Not really up on prices of the 5 and 6 speeds. Have heard of picking up a viper trans for 1000-1500 dollars though.
As for od options for Hemi or la ya have the 500,518, guess you could use a challenger trans,gear vendors, GM 200r, GM 700r the one you listed and there is even a kit for a ford aod out there. The expense come when using a non mopar trans is the adapter kits. Some are $800. Gear vendors is close to 3k.
All of those transmissions also need the torsion bar crossmember cut and modified which some guys don't want to do.