Check out http://www.mobark.com, http://www.seequipment.com and http://www.banditchippers.com. Those will give you a good insight to the chipper mfg's and a used equipment dealer. The answer to the other is how big a limb and how fast do you want it chipped is directly related to ther price. I've seen a few 4" chippers go for around $3500 and up. There is an 8" chipper here in town with hydraulic feed for $15,000, and its a late model unit.
3 years ago I bought a 1994 Brush Bandit model 90 (9" capicity) with a 50 HP Perkins. It had aprox. 250 hours and cost $10,000. It now has 600 hours and should sell for $7500 if I sold it to a dealer. Eric