I don't know how you define cheap; but you can buy deer antler from www.woodturnerscatalog.com . I would bet that if you did an Internet search, you could find loads of places that sell deer antlers.
If you have friends who are hunters, check with them(or maybe a local hunting club). Not every buck that is harvested is a trophy. Also hunters sometimes find antlers that have been shed. Offer to trade a pen.....antler, of course.... for a supply of raw marerials.