Which specific asthma inhalers are you referring to? Generic albuterol inhalers are available for $27 cash price, or less if you have health plan coverage.
Obesity obviously doesn't cause high drug costs but it is a risk factor for asthma. Non-obese people are less likely to have to spend anything on inhalers.
The argument here is that the US will have worse health outcomes than another country because the people are less healthy. Cost of care doesn't factor into this argument.