Hot wire cutting foam-Stainless steel
A Variac is my choice for a power supply. I never have used it over 16 volts. I prefer to use .014 solid music wire for cutting foam. If you need music wire that is under 36" long it can be obtained at hobby shops. If you need longer music wire try a hardware store that carries Malin's music wire. Malin Co. is located in Brook Park Ohio. I have never had much luck with nicrome wire due to the stretch. The welding wire and fishing leader sounds like a good source also.
A good source for a good used Variac are Ham Radio Fests. These guys have used them on their radios to boos power or to warm the radio tubes up before applying full voltage. I have never been to a Ham fest without seeing a few good ones for sale. Usually between $20.00 and $30.00 Type in Variac on the Google search engine and you will get a variety of choices also.