http://www.jffjewelersupply.com/ JFF in suburban Atlanta has superb service. Just pick up the phone & call them. They sell based on spot prices, not like Fire Mountain. Your big overhead would be postage with them. They have sterling, argentium, and gold filled, wire, sheets and possibly more - this is the only stuff I have price sheets on. They also carry a full line of jewelry tools and machinery. Very nice people, knowledgable and willing to explain everything.
I am LOVING their fine silver. I bought some that is like thread! 30 gauge? I haven't used it yet, but I ran over & stocked up when silver dropped to $28.50!
Ace Hardware - THE place for plain copper wire, hands down. Prices vary from Ace to Ace, though, but they have a great selection, and it's much cheaper than Michaels. If you want the heavy gauges, ask for ground wire. It is sold by the foot. My Ace guys now call it bracelet wire, LOL!
SOME Walmart stores get in silver plate but alas not all, and it seems to go fast.
There are many sellers here on Etsy with excellent prices on most wire. Unkamen has a huge inventory! I haven't ordered from him yet since I found him after I had bought off line from a former eBay seller.