i brought 4 this year from, one ca-42 from dealextreme at $4.44 (shipping incl), this is the one i used for the spectrum analyzer.
http://www.dealextreme.com/details.dx/sku.446
another two ca-42 from two different ebay sellers ($2.00, each, shipping incl), one more dku-5 from ebay, i was trying to find those older types that has 4/5 wires (Vcc incl.) but to my disappointment, all are the same inside, 3 wires having the same pcb.
if u get them, i can provide a short write-up / diagrams to show the best way to hack and use it. w/o any modification u can immediately use it (free from