There are at least two arguments in favor of ability to keep Russian launches cheap(er).
First if mentioned in John Clark's "Ignition!", where he says that the Russian approach to bigger payload isn't the technology, but just the size of the rocket - with same low-tech as something smaller. So, in other words, technological edges aren't always translating into lower costs in this industry.
Second is Russian's technological edges with kerosene liquid fuel engines. Technologies are well-optimized, including costs, and are the primary used ones for Russian space program. Not solid rockets, not hydrogen - and comparatively little hydrazin-based rockets, at least by the number of launches.
As an aside, solid rockets is perhaps the part that disappointed me most about "Ignition!". I guess it shows its age. Do you know of any reading about their development? Couldn't find much on Wikipedia...
Well, this is the best public Russian space forum. Won't get any better in Russian, with all Russian sources.
So - yes, I agree that the information sources are limited. But at least you can try to trace the original sources from posts there.
On the original question, I haven't seen a comparison of actual SpaceX launch prices with actual launch prices used by other launch providers, specifically Russian ones. With Russians it could be useful to check both "commercial" and "federal" launch prices, as the first are driven by market, while second are more driven by actual costs.
As for the 'tech', yes the Russians have a long and pretty good history with rocketry but SpaceX has technological edges as well.