[chriscolombo]

Although Delta ranks in my book as the worst of the worst, the rules pertaining to non-refundable tickets are fairly standardized. Delta charges $150 to apply an unused nonrefundable ticket to another flight. Whether you pay $100 or $1,000 for your ticket at delta.com, it still costs $150 to use it towards another non-refundable ticket. The change fee is irrespective of the cost of your fare.
The condition of being non-refundable is in exchange for a deeply discounted ticket. You said you only paid $100, but had you purchased a fully refundable fare for the same route, your ticket would have been far more expensive. The good news is you only lost $100. I wouldn't worry about it. If you do need to buy an airline ticket, it can still be applied to another ticket (plus change fee) for one year from date of purchase. Unfortunately, Delta is not alone in this scam. Airlines have been doing it for decades. Delta just handles it a little worse than other carriers.