Someone wrote a nice guide on it.
The GTN can be reasonable for low ish level greens. People will usually list them at less than default price....which still puts it above what they would get if they just vendored the item(selling it to an NPC).
Even just buying a couple pieces at level will help. Heck, if your stats are that far askew from your intended main stat, it might actually help to buy gear more than a few levels below your level. Then, get out questing or run a flashpoint to catch up your gear level.