What to charge for traveling with a client to a seminar

I am looking for some feedback about what other Quickbooks ProAdvisors charge for their time to travel out of town with a client.  My client wants me to attend a budgeting seminar for his industry with him so we can directly apply the information for his business. He is willing to pay for time + expenses but I'm not sure what is an appropriate to charge him.  Has anyone traveled with a client and billed for their time?