The modules are priced as they are for a variety of reasons. Here are just a few:
Small batches are expensive
We build these things in batches of ~500 tops because we don't know what our demand is going to be, and because we're a tiny company with limited resources. This necessarily makes them more expensive than anything mass produced.
When we first launched the platform, we didn't want people to make decisions based on price differences of a few dollars. That is to say, we priced modules in two tiers, in the hopes that the message of "these two things will get you the same amount of utility and fun, so don't deprive yourself for the sake of a cup of coffee."
Convenience and support
At the end of the day, you're paying a little extra so that we here at Technical Machine were able to vet the part, write the driver, support you in your use of it, and package the whole thing in such a way that is plug and play and requires literally zero electronics knowledge.
If you'd rather design your own stuff or spend fewer dollars on a breakout board from someone else, then a few bucks on jumpers, then spend time writing a driver, that's your call. We find that most people agree that their time saved and satisfaction gained are worth the extra cost.
All that said, some things will change as we move towards Tessel 2. While I don't know if prices on existing hardware will drop too much (a lot depends on our contract manufacturer here), we will be replacing modules like Camera, GPRS, Audio, Bluetooth, and possibly GPS with off the shelf USB variants, which will make adding those capabilities to your Tessellation a lot cheaper.