They earn more than season workers in Italy or Spain that's for sure.
Qataris pay around 10$ p/day to construction workers, minimum wage
law in Qatar. 275$ a month. All this after protests from workers, who were paid as low as 0.5$ p/hour when the stadium constructions started.
Seasonal workers in Spain and Italy are paid 7€ p/hour, the minimum wage. Around 1000€ a month.
Of course we should take into consideration the country of origin of those workers both in Qatar and EU, living costs in their respective countries and such. They all send money back home.
So, overall, attending a full WC tournament to see Cristiano and Messi will cost a lot for those workers.