Numbers for cost of kilos of cargo to orbit are so hard to get it is likely impossible to answer.
For example, what is the cost of a Shuttle launch? Well, what do you include? Numbers have ranged between \$500 million to \$2 billion. That is a fairly large range of numbers.
Any time a national program is involved, there are many hidden costs that are very hard to attribute properly.
The Russian program is a great example where it is not clear they need to actually make money and cover costs.
Very few commercial launchers have real price lists, there is always a deal, or some detail.
The ULA example is interesting. While the US military just did a bulk buy of 36 cores for a theoretically fixed cost, it should be easy, right? But what about the ongoing billion dollars a year they get as ongoing funds for the program? Does that count into the cost?
Does the cost of the range get added? Air Force runs the range in Kennedy/Canaveral, should their costs be included in costs?
Even SpaceX which is theoretically posting prices, \$56 million for 28,990lbs to orbit, suggests \$1931/lb, or \$4,248.2/kilo which is pretty low. But then consider the contract with NASA for cargo to the ISS at $1.6 billion for 20,000 kilos of up mass. Which comes out to closer to \$80,000/kilo which seems ridiculous in comparison to the raw cost. But of course some of that money was designed to spur development and let the next contract be more affordable.
Of course you need to normalize orbits for payload capacity to get a comparable cost.
But there are overall trends. Government run, national prestige systems (Space Shuttle, JAXA H-2A/B, ESA Vega) do not really need to be cost effective. They exist for political reasons, darn the costs. These have no incentive to get cheaper, so have not.
The Russians were desperate for foreign currency, and were willing to sell anything at any price they could manage. China took a similar approach initially. Whether they make or lose money on these deals is very opaque.
The best news is that Antares from Orbital, and Falcon 9 from SpaceX have a goal of actually making money so they are incentivized to actually reduce costs and run an actual business.
Time will tell, but the new entrants give us hope.