yes, HAZMAT and non HAZMAT stuff ship on the same truck and are even on the same paperwork but that isn't the cost factor. The whole system is expensive, all the paperwork for just the HAZMAT items, the training and extra insurance plus the extra scrutiny the company and drivers go through on a daily basis. There are Federal regulations and regular inspections of the papers and facilities to put up with too. Permits in almost every state that you operate in are required too. I have to have a FBI background check whenever I renew my drivers license and I have to pay for that.
If you look on Gunbroker and see all these private parties selling powder and primers, there has to be a majority of that shipped by the USPS in priority mail packages unknown to the USPS and we all know how bad some of the packages we receive are handled when we get them.