As a long time self employed contractor in another industry which is prone to lots of people undercharging (because there are many people who dabble and few who try to make a living), now married to someone whose CDL is part of their job. Do not undercharge shipping. That is a favor that does no one any good in the long run. It undervalues your work, your time, and your sunk costs; it shocks the client when they have to pay the actual costs; and it makes the life of the person who does shipping/trucking as their primary job that much harder.
If you do not want to charge the actual rate, make the discount very, very clear. That is: shipping costs are X but because you are my training client, your shipping cost is discounted to Y.
In general a CDL driver should be making 30 cents or more to the mile. Which is On TOP of the regular cost of running the vehicle (the IRS mileage standard). Complicated shipping, which I would consider horses to be, but not as complicated as hazardous or oversize freight, ought to be more. and that 30 cents is on the ‘Swift’ low end, it really ought to be 60 cents to the mile. In joke: (Swift, a major carrier on the east coast, is known to stand for: ‘see what I f— today’)