your local generator rewind shop or auto alternator repair shop is a good source for free wire , if you are willing to work for it.
the only tools you need are a dremmel w/a abrasive wheel attachment
they throw large starter relays out in the junk everyday
inside you will find an outer layer of ~20ga. wire , and an inner layer of 17 to 15 ga wire depending on the size of the relay
these are bigger than your average car starter relays , which may also have some useful wire in there
the first picture is an average sized solenoid
the metal case is crimped around the bake o'lite(sp) at the upper part where the metal meets the bakeOlite , thats where you dremmel right on the curved part , i've gotten pretty good at it by now and can cut the lip off of one in a few minutes
once you get the lip off just hit the bottom part with a hammer and the wire pops out all wound on a spool , like on the right , which is the outer layer BTW ~20 ga.
beneath that is about 50 feet of 17 ga wire all wrapped nicely around the spool you see there.

