If you are going to do a show why not just have your partner acompany you in a Paso Doble routine? instead of a cape?
I searched the net with key words "bullfighter" and "matador" to find a few useful pictures. In the MSN encarta bullfighter section showed a few pictures that the cape is actually quite huge. Some costume sites didn't provide the dimention of making such capes, however.
This is a costume I made from a $5.00 suit I bought from Salvation Army shrift store. A few rolls of lace and some fabric adheresive did the trick. Total costs under $15.00, but spent many hours of my time creating it though. ;-p