David, I would recommend the Neutec casting machines from Rio. First
they are made here in the US so you won't have any problems getting
parts and supplies. Second they are very well made.
Memco units are not as good as the Neutec machines and Memco wants an
arm and leg for parts and supplies.
All the others are made outside the US and you will find very quickly
you've spent several thousand $ on a machine that sits in a corner
waiting on parts more than it is use for production.
Next, You reference to a 'coil' heating chamber is a resistance
melting machine and not an induction machine.
Resistance machines are much less than induction but are not nearly
as fast. For instance the Neutec J2r is a resistance machine and it
will take about 30 min. to melt your metal for each batch. The
induction machines will melt in a couple of minutes.
I'm not a big fan of Rio for many reasons but they do make the best
induction melting machines.