The actual payload and range of the Mi-8 put it exactly in the S-61/S-92 class.
The biggest reason for the lower prices per hour is the state of the Russian economy, as well as that of the former client states that carry enormous amounts of spares, willing to sell them for literally cents on the dollar. There is nothing inherently "unsafe" about the classic Russian designs, but there is much that simply does not meet the standard of a modern western helo. The design philosophy was to build rugged, cheap to buy, cheap to operate military aircraft (the "civil" models have a paint job) that did a good job of ferrying hundreds of thousands of troops in battle. The massive Russian war machine was equipped with about 5,000 operational Mi-8's and about half that of Mi-24 gunships.
The overhaul times are awful, the airworthiness control of spares is practically nil (Chinese knockoffs made in bicycle factories are world-wide nightmare for the Mil guys) and their accident rate is eye-watering. They are used in the former Soviet client states because that is what they are used to and what they can afford (a legacy of how very successful Communism was, frankly, to everyone who embraced it!)
I have the deepest respect for the folks who made these machines (I am friends with Dr. Marat Tischenko, chief designer of the Mi family for 2 decades and Gorgen Karapetyan, their former chief pilot). The newest generation of Russian designs will have the design features, certification basis and maintenance controls to compete world-wide, I am sure.