Where are you located? I completely understand not charging as much as we do but you can make more. They need it done and would pay somebody 75 to mow that same size yard here. Charge more make more means you get better equipment faster. I wouldn't want to make $18 a hour to be out in the heat while they are probably sitting inside in the ac watching you sweat your butt off.
On another note you seem like your picking up yards pretty consistently. Do you work a job during the day?