Hi,
just an fyi, but I just purchased from these guys http://www.rcuniverse.com/market/item.cfm?itemId=598074 and needed several of the 24 inch and 18 inch extentions and I couldnt make them for 3 bucks a piece. They use HD diameter wire,gold plated connectors , its silicone insulated and twisted to boot... and FREE SHIPPING also! They do sell the wire by itself ( I was thinking of doing the same as you by making my extentions, they sell the wire at $1.00 per foot), but then you would need to purchase the connectors and the crimping pliers also, so for me, this was the best way. If you need some longer pieces, I think they go up to 36 inches for $3.00 a pop, but probablly would make any length you requested if longer than that.
Hope this help you,
John