A very helpful youngin' over at Hammock Forums by the handle "the scouter" compiled a spreadsheet[1] that compares the prices of various DIY/MYOG fabric suppliers. I found a few minor errors, but overall it's very useful. Scott (I think he posts here too) at DIYGearSupply[2] née BackWoods DayDreamer is really holding it down in offering great prices.
It may not be the case, but it looks as if Scott's decision to only offer one to a few colors of each fabric really drives his prices down compared to the other shops that offer a wider variety.
[1] https://spreadsheets.google.com/spreadsheet/ccc?key=0Aq6B5SHKA8kUdEZMbnJ4bUYycDBFZldIYzQ4YzRlYUE&hl=en_US#gid=0
[2] http://www.diygearsupply.com/cgi-bin/isle.cgi?type=all

