My first cosplay cost about $250. Extensive wig work (base wig, extensions, extension making materials), armor (craft foam), contacts, bodysuit (for decency), shoes, and other small things (clay, exacto blades, etc) all managed to raise the cost. Of course, I didn't know what I was doing back then, but it still would have been a massive chunk of cash.
My costumes now go from $70+, mainly because I have most of the supplies on hand already- which is generally the biggest drain of money when you are the only one in your family/friends who does this sort of thing.
Currently in the works:
~Taokaka, alt colors~ (90%)
~Syaoran, Tsubasa: RC~ (base planned, staff 50%)
~Novice Mage, Skyrim (base planned, props 50%)
~Sheeda/Caeda, Fire Emblem: Shadow Dragon(base planned, prop planned)