So, to make a completely logical argument here, the real money "price" of ships, i.e. the amount of money you have to back the game for to get a certain ship as a thank you is completely off the scale of what ships will have to cost in the end. Ship prices should increase exponentially with size, not increase in size exponentially by cost, that's just a pure basic for progression and balance.
Don't believe me? Look at it this way, in a normal RPG (as well as in real life usually) the time you have to put in to increase in level goes up with each level so that it feels like more and more of an accomplishment. Now compare this with the current state of SC ship prices:
Let's just make a really crude example where cargo capacity is a direct measurement of how much money a ship can earn you and let's put the base at an Aurora MR "worth" $20, Cargo Capacity 13. Say it takes you 1 standard unit of time to gain enough to upgrade to a Freelancer at 5.5 times the price and 4 times the cargo capacity. Just taking the next step from there you would gain 22 times the cost of an Aurora MR in the next standard unit of time, or 4 times the Freelancer. Now we're past a Starfarer even with the new cost, we can almost buy 2. But say we get one and use it purely for cargo hauling, it has over 255 times the cargo capacity of an Aurora MR, so you'd be able to buy two javelins with margin after one standard time unit with that. It just wouldn't work, even with increased upkeep for the ships and everything they are way too cheap relatively each other now and that price is not meant to represent the final price in game, it just can't be. And please make note here that I use cargo as an example and am not even touching the pure cargo ships, because the scale would be even worse then.
The low price now is a huge thank you to people who believe in CIG and back the game early and it will give us a huuuuuge head start once the game goes live.
Once ships actually gets done and able to fly they HAVE to increase the price of the larger one, otherwise the game balance will be broken beyond reapair. Once in game, the starfarer can't even be on the same scale price wise as auroras.
Also, it's a lot about starting balance, they have to keep the big tankers relatively rare as to not oversaturate the market.... if a ship becomes too common they HAVE to increase the price or not sell it at all again... and I think the price hike is the one that leads to the least complaints.
Remember, you're backing development, not buying the ships. The ships you get is a thank you and the value of them increase exponentially with how much you back at the moment, this is not how the final economy is supposed to work but is a token of appreciation. Unfortunately there's a limit of the appreciation they can show if they ever want the game to be balanced. It's not because they don't love us, it's because we showed them more love than they can handle.
