Go to the local pharmacy that is not walmart or walgreens, the one down on the corner that's been there for a hundred years...Talk to the pharmacist and ask them if they have children's liquid Sudafed.
I buy it for about $3 at our local pharmacy. Since it's liquid I can control the doses myself and feel better about how much I am adding to their little bodies. You might just call around. Since you are close to a big city you may have to call and ask lots of pharmacists. Don't believe a pharmacy tech but ask the pharmacist themselves if possible. Ask them to look it up. I have had arguments with the ones at Walmart who "KNOW" that it was taken off the market years ago...I just bought some last week. They had to order it because they were out. They can get it, they just may not want to.
I also use it for sinus congestion and the dose for me is 2 tsp. and I have never tool more that 1 tsp at a time. It is just too much medication. So I am perfectly able to function on 1/2 - 1 tsp.
Sudafed does help with the chest congestion by making the mucus going down into the lungs thinner and runnier. So it's less likely to gather in the lungs and be really thick.
We use Tussin, which is Guafinisen in the list of ingredients, from Walmart. We use the Sudafed then 2 hours later we use the Tussin, then 2 hours later the Sudafed again. Etc....