How can I help my childs allergies?

My (almost) 4 year old has terrible allergies. The doctor wanted to prescribe her singulair, but the co pay is so expensive (bad insurance) that there is no way I can pay for it. There arent many choices for children allergy meds out there either. Bendryl works but of course makes her sleepy so I cant give it to her during the day. Ive been using childrens zyrtec lately, which says its supposed to last 24 hours but it really doesnt. It seems to help but its not a huge difference; it helps with the allergies but doesnt get rid of the congestion. She has become a mouth breather all day long, especially at night and its causing bad breath and a white coating on her tongue. I feel terrible for her! Any suggestions to help my poor girl??? Thank you!