For a power supply, I'd considered several options.

A bench supply can be directly used, with advantage of using constant current mode.  While I have several, they are all larger and set up at my bench, not convenient to move around.  As cutting needs to be done in a well ventilated area, moving one of these to the garage every time would be a nuisance.

There are quite a few lower cost switch mode power supplies which could be used.  I would prefer to use things from my stock however.  This model for  $50 seems like good capability, though I'd still need to dig up a ac-dc supply with sufficient voltage and current and a case.

A battery powered solution would be to use a moderate or larger size hobby lipo battery(3 or more cell, 2000+mah).  A brushed motor speed controller can be used to regulate the power, and a servo tester used to control the speed controller.  

I could also make my own, which I've also decided to explore, given all the stock of parts I have.

Needs

This table from http://hotwirefoamcutterinfo.com/Introduction.html is super helpful for estimating the current and voltage needed for various wires.  Unfortunately it doesn't go out to the wire length I need for the bow, but having the resistance table and needed currents are the key, and can easily sort out the voltage for a given wire length.