Agreed. Without wanting to be boring about this (but I used to run a removals company, so I will be), unless you advise your insurance company you’re doing this your insurance will likely be invalidated. You’re driving for hire, which has high associated risks.
Secondly, what happens if the instruments are damaged or stolen when in your possession? Without appropriate insurance you’re taking a huge risk, particular with high value instruments.
There’s a reason that courier costs are high, and it’s not because people are particularly greedy.
I wish you well in your endeavour.