A 93 ssei can go down to about 2.2 for a pulley size. You have a 2.5 stock pulley. Best place to get the pulley is from www.pulleyboys.com
Pulley is about $100.
You can get the coupler from www.zzperformance.com
Coupler was about $20-$30 if I remember right. Same one fites both the m62 and m90 superchargers (you have the m62). There is only one size coupler, no changeing it for different pulley sizes.
Not sure how much shorter the belt will need to be, I'm guessing 1/2 - 1 inch shorter, depending on the pulley. Best bought from the local parts store. Belts about $25 - $45 depending on brand and such.
All the parts should run about $145 - $175 for everything. But keep in mind you will also need sealants, gaskets, and cleaners to do it right so add another $100 roughly for all that.