If you make 5k before taxes you're already way above average here, because your employer usually pays around 7k per month then.
Edit: Yes, I admit it is quite low when compared against typical contracting rates in urban areas.
Normalise that to €60k per year. Full-time work in Germany is 231 days (52 * 5, less 29 days legally-mandated holiday).
€60k / 231 = €259.74 per day.
So around €260/$290/£220 per day. This is definitely the low-end of freelancing/contracting rates in Germany[1]/Western Europe.
[1] Contracting rates in Germany: http://forums.contractoruk.com/business-contracts/77870-hour... (German)
http://www.schulferien.org/Arbeitstage/arbeitstage-2016.html
Your general point still stands: 30k is a low contracting rate and in general untenable for a freelancer. You should be earning at least twice as much. However, for open source work this is a major step up - you can make a living off it instead of self-funding your work.
If you make €60K you are very good for beeing a self employed (programmer) and make more money than many not self employed programmers (yes, even when you subtract all taxes, health insurance and your private retirement arrangements).
Specialists in big corporates earn of course more (what GULP is targeting), but then at first place you have to be a specialist and need to have the expertise.
Also don't forget that many people do not have work the whole time... so you have to see the GULP rates also in contrast to gap times where you have no income.