i dont really know about the rest of the world but to me i use the standered fee rule
(a full time jobs pay/day in work/hours per day)x1.5= freelance work fee
for here it ends up:
($1,200 US/24/8)x1.5=$9.375
and then i use what i call experience boost
(freelance work fee) x (1+(number of previous jobs/100))= current rate
so for example i have had 80 jobs lets say:
(49.375)x(1+(80/100))=$16.875
thats how i do it currently here in Palestine where the minium wage is about $1US/hour and i am still a student that is in college and i work out of my apartment. in the end it works for me so i think every one must find there own way and the more experience the better