$500 tops for a complete running engine pan to carb with all brackets and pulleys. starter also. that is all i would pay and that is top dollar. i gave $450 cash for a magnum 360 with a verified mileage of 86k. watched them do a comp. test. was complete engine. exhaust manifolds and flex plate included.
When I was looking for one about 3 years ago they all seemed to be in the $250-600 range around south east WI. After watching craigslist for a couple weeks I ended up buying a complete low mileage 360 with transmission from a running '77 charger for $450. Then I sold the trans and all the accessories and stuff I didn't need for $300.
I am going to say $500 tops also. I gave $200 for a great 360 that had a Ramcharger wrapped around it and I drove it home so needless to say things vary.
Whatevwer you're willing to pay. If someone is there and willing to pay more, they'll get it. I've gotten great runners with transmissions for free, and I've paid $3-400 for them alone. Last one I sold as a runner was $450.