Right now they're essentially growing tomatoes and selling them for $15/gram. There are 450 grams in a pound, and tomatoes generally sell for about $3/pound around here. Let's assume for argument's sake super high end heirloom tomatoes grown indoors at $15/pound. They're growing selling their product for $6750/pound, let's round down to $4000 since some people buy in bulk. They should be making so much damn money it's ridiculous. That's a very conservative 26000% inflated price over someone growing a slightly different plant (and still making a profit). Their profit margin is HUGE.
While tomatoes and cannabis are very similar to grow, the yield of usable product is not even remotely the same. From an area where I could expect to yield a pound of high quality cannabis, the equivalent amount of space with tomato plants would probably yield me 20-30 pounds of tomatoes. So a direct weight to weight comparison is not valid.
That said there still is a huge amount of waste and inefficiency in the growing process, along with greed. If you can produce cannabis for $30/oz, but the market will bear a price of $200/oz, what are you going to sell it for? I've seen this a lot in the medical marijuana industry in michigan. The black market price was about $200/oz, and when the medical marijuana laws got passed in 2008 I saw the quality of product increase (much more high quality indoor product available as opposed to low quality outdoor mexican grown product), and the availability of product increase (everyone in michigan got their medical card and started growing), but the price actually increased (always justified as being higher quality) despite taking most of the illegality/risk out of the equation.
There is also a huge difference in production cost between outdoors vs indoor. Indoors allows much better control of the environment, and in the end a much higher quality product. But that comes at a steep cost as space, and energy are at a premium. A pound of indoor marijuana will probably cost around $150 worth of electricity just to run the lights. Very few people grow vegetables indoors using non-solar light because it simply isn't economical compared with using the sun.
EDIT: I do think legalization and commercialization can and will drive the price much much lower in the future than what it is right now, but it will never (and for reasons I stated, never can even in theory) be priced on par with tomatoes on a weight basis.