please refer to this incredible thread regarding DIY interconnects DIY interconnect review
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I don't have any experience with Mogami 2803 but have made several pair of interconnects with Mogami 2534 Neglex Quad microphone cable. It's very easy to work with, thin, flexible and copper shielded. It's got four 24 gauge conductors so doubling them up gives you the equivalent of 21 gauge.
It's available from takefiveaudio.com for about $1.15 a foot or markertek.com for about $.80 a foot.
You may already be set up with supplies to make the cables but if you need to buy solder for the job I can recommend the Welborne Labs TLS silver solder available here, http://www.welbornelabs.com/solder.htm. It's inexpensive and I've found it very easy to work with. It's not a major consideration but when you're working with very small components and trying to apply enough heat to make a good joint but not so much that the insulation starts melting, good solder makes the job a lot easier.