You should do one or both of the following:
-
Bill a lower rate for travel. If your normal rate is $100, charge $60 or so/hr* to travel. Like it or not, this is still time you must invest that prevents you from doing other billable work or searching for other clients, and as such the time has value, even if it is just travel time. Plumbers charge for travel, lawyers charge for travel, etc. That said, consider whether skype or other alternatives are useful. If this is a sales call don’t bill.
-
If charging for mileage is in your contract, charge it. Don’t create an ambiguous “will they or won’t they” situation for your client re your billing. Keep it simple and do what you say you’ll do.
That said, when you are working with a remote client, you will need to travel. Establish travel expectations (distance, frequency, purpose) in advance so you can build your program fees appropriately. Don’t bill retroactively.
*the thought being that if you are freelancing, your hours target is probably something like 1200/yr, or about 60% of 2000 hours. 60% of your rate (@ $100 above) is $60 - what you’d need to make if you were 100% billable and could afford to work at a discount.