Craigslist.com or ModelMayhem.com are great resources for nude models. You should get a model release, but should not need a formal contract. Price range is going to be around $75-100/hr for nude models. However you can sometimes find less expensive models who are new to modelling.
Well, you could start with modelling sites like Model Mayhem, and see who might be listed in your area. I would think that, as long as you've got money willing to pay, there will be models willing to work with you. Once you find someone both interesting and interested, you should probably meet and hammer out the details from there.
You may ask some local drawing schools, they hire models too. Or maybe do some "less controversial" sessions to your friends and their friends, and when you prove them that you are serious and skilled photographer, they will be more eager to pose nude.