From the beginning of the Principate, aka after Augustus (Octavian) to the Dominate, and to the end.
I'm looking for such a work. The Oxford History of Rome is shite, disjointed and mishmashed, and the Cambridge dish offers little more. I saw a good Blackwell treatment of the later Roman Empire, but it doesn't cover anything earlier than AD 284, which is well into the Empire proper. I refer to this volume: http://www.amazon.com/History-Later-...=3QGTPDT9YLOD7 which apparently treats both Eastern and Western Empires, something impressive in its own right no doubt, but seeing as all I've read on the Romans reaches but the end of the Republic (c. 44 BC) it leaves a considerable gap (44 BC to AD 284) which needs coverage.
Price range: 15-20-35 dollars maximum of the maximums.