"Basically a SSD is just a bunch of flash chips, with each chip providing a specific amount of storage space. Larger SSDs require more of these chips. These flash memory chips are built using 32nm and 45nm manufacturing processes on silicon, similar to CPUs. However, flash memory isnt as complicated as a CPU and there are things like multi-level cell storage that flash uses to fit more data into a smaller space, so the cost isnt quite as much as a CPU. Still, it takes several flash chips to provide the storage for an SSD. Additionally SSDs have additional components that add to the cost. For example chips that handle the flow of data to and from the flash memory. Some SSDs have extra flash storage that you dont know about, because it is there on standby in case some of the flash memory goes bad and can replace the bad memory, so that as a user of the drive you dont know something has gone wrong. The process of making these chips is expensive. Even if a single chip can hold 16 GB of data, it will take 4 of these to make a 64 GB SSD, and if you use the price of a really cheap CPU as a benchmark, then you are talking about $30 at least per chip. So thats $120 just for the flash memory on the drive and that doesnt include the extra components that comprise the drive.
So it is a matter of the process of making flash memory is expensive. The other big factor is storage density. HDD manufacturers have managed to continually evolve hard drives such that they can fit more data in the same space, and thus similar manufacturing processes can produce more storage. For flash memory chips to get cheaper, manufacturers have to figure out how they can use the same/similar manufacturing processes but instead fit more storage space into the same flash memory chip. Increasing the storage density of the chip will make the cost per gigabyte of storage lower, since you are producing a chip with more storage using the same manufacturing process. So your manufacturing costs dont go up significantly, but the amount of storage youre producing does. The issue here is that increasing the storage density on silicon involves significant technology challenges to make the components of the chip smaller. The 45 nm and 32 nm processes currently used are named for the size of features on the chip, and making these features smaller so that more can be fit on the chip is a really difficult challenge."
It's mainly because they are "new" on the market still. They actually are most likely cheaper (Maybe?) to manufacture than a traditional hard drive. Right now, it's all about them being new and popular, so they are high priced. Give it time, they will become fairly cheap within the next 2-3 years. Just the other day I was on Newegg, and couldn't believe that a 1TB hard drive is only $55. Heck, I remember just a few years ago, I paid $129.99 for a 40GB drive.
One problem with SSDs is that price increases almost linear.
HDDs general cost almost the same no matter the capacity. 1-4 platter but there aren't nearly as expensive to manufacture as building silicon chips.
It is like manufacturing a bunch of CPUs that simply is expensive even if is very cheap and simple CPUs.
Additionally the more they shrink the flash the worse they get and more capacity has to be set aside.
50nm MLC hat 10000 earse cycles. 34nm is said to be around 5000 and 25nm is still half of it. HDDs don't have that problem.
Many people are dreaming of HDD prices which they will not reach for a while. The only thing one needs is enough space for a reasonable price. I wait for >250GB SSD for around 200-300 $ and that would be worth it for me.
You just have to get away from the idea of paying per GB but understand you are paying for speed and all you need is enough space. For pure storage HDDs are cheaper and will be a while.
R&D, manufacturing setup, licencing, fixed & variable costs, break-even, effects of competition, supply/demand curves, consumer choices, economies of scale, law of diminishing returns, ... I think this question is best served by an economics course.
I heard, but can't confirm that standard hard drives will be around for at least 5 more years. Something about making sure that SSDs can hold the true test of time. Heck, I have old, enormous 5.25" hard drives that still work to this day. Slow as molasses and only 5-20MB each, but still work.