DZK sells them on RPS for $75 including shipping, I got mine form him and it's awesome! You can install the U/D pulley if you change your belt, BUT YOU WILL NEED A SMALLER BELT (run a search on RPS for the correct size or check out RangerBill's site)! You simply take off the old U/D pulley (very bottom pulley, 4 screws) and install the new one. It's best to install an electric fan at the same time, since the ol' clutch fan will keep hitting your knuckles when you remove and install the pulley. You'll notice more power, especially at higher RPM's.
Note: If you have a big sound system, lotsa offroad lights or a lot of accessories running off the battery, I'd get a more powerful alternator (Tremor to 200AMP, XLT to 130AMP...might have to read your current to make sure). This is because your alternator won't be charging as much with the smaller pulley.
1999 Ranger XLT, 3.0
2000 Honda VFR 800FI