I bought a 3 pack of SP5's because they were only $20, plus the cost of cables. But the SP4 includes the cable and looks like a deal for $10. You may want to consider a mic stand as well. MF has some good deals. I checked out the Shure SM58 and it didn't sound any better than the mic that came with my Karaoke player so I took it back and got 3 SP5s, cables and a mic stand about $60.
http://www.musiciansfriend.com/produ...one?sku=277516