[SuperCreeper007]

1) Last time I went to the DE, mainly to let /kill wear off, I saw glowstone was @ 2k/stack. I'll take a few stacks, please
2) I'm selling sand in bulk here: http://minerealm.com/community/viewtopic.php?f=8&t=7706, @ 10/stack, which means 40/stack for sandstone.

[DrHetterscheidt]

The market decides the price. Though there are many (too many) instances of somebody citing another source as to why their prices are the way they are, people will buy what they want to buy. If it's too high, don't buy it, and the price will go down. If people are buying it, then the market established that it's a fair price to pay.
You can also expect there to be constant inflation for every item as people typically get richer by the second. Renewable resources SHOULD be cheap, as supply should readily exceed demand. But again, the market will create the results.