I would think $9 includes the insurance cost for a $20-$30 45, not out of line.
The days of cheap postage rates are long gone.
It costs around $12-14 to send one 45rpm disc across the USA via priority mail. I just mailed one to New York, maybe 100 miles from my house, and it cost $6.50 uninsured.
I would never opt for a cheap cost, media mail transport in the USA for records. I've witnessed the sorting methods first-hand in a postal distribution center. Even for 1st class packages are subject to potential damage. I'm amazed parcels usually arrive to their destinations intact. I've seen some mashed up/ dinged / crushed parcels make their way from the cross-dock after being sorted and processed.
Priority mail parcels (small size) are not sorted with 1st class, media mail or parcel post packages and tend to be hand-sorted.