Using the lost wax process what you cast is not limited to the melting point of the metal or alloy but to the material around the wax.
Aluminium could be the most difficult as its not that heavy and most lost wax processes for rings and dentistry use a melt and centrifuge process to actually cast the metal.
Stainless can be used as it is used in dentistry and that melts at about 1363C
The most time consuming would be cnc unless you are going to make lots of them just producing the code would be quite onerous.

Peter