Best way to say that I charge for coming to you?

In the United States this is known as travel and expenses and often abbreviated T&E. As Michael pointed out, you want to fully disclose your policies up front so that there will be no surprises later.

You may want to use something like this:

Travel time will be billed at the rate of $50 per hour and the client will be charge for all related expenses including but not limited to mileage at the rate of $0.51 per mile as well as all tolls and parking fees. Should overnight travel be required all meals and hotel expenses will be the responsibility of the client and the travel time expense shall be capped at $400 per day.

You can say, "So there are no surprises for you later, I would like to let you know that there are associated charges with coming to you. I hope this is okay."

It's commonly called a trip charge or a service call fee. It is unnecessary to say that it includes your expenses such as fuel because virtually everyone expects the business operator to pay for such expenses as overhead.

Consumers and small businesses usually don't want to pay this type of fee. One thing you need to decide is if the trip fee is included in any on-site activities. So once you are there, and you effect a repair, the customer is simply charged the cost of the repair.

The trip charge is usually only charged for unproductive service calls that are the fault of the customer - such as not being home when you arrive, or cancellations after you arrive, or an outright obvious customer error such as having a device unplugged.

I tried operating an on site computer repair service a few years ago. The problem I chronically had was that no-one took my fee schedule (including a trip charge for visit) seriously. Essentially the problem is that I would invest the afternoon in the service call which turned out to be unnecessary and the customer would not pay me the service call fee.

I "fixed" this problem by demanding for new customers - especially for service requests that were quite likely to be unproductive - that I bill them via PayPal and that fee would be credited to any repairs actually performed. So pre-payment was necessary before I would make the trip.

It was always rejected, but at least I could say that "yes, I will come to you, but I am not driving 50+ miles to your location to tinker at my own risk." It was really my way to reject such customers as poor risks but to do so in a way that was not explicitly insulting.

This leads to one last point. You need to decide if you even WANT this type of business. In my view, customer site visits to perform repair or other technical service work are high-stress, low-reward events with a high probability of failure.

For computer repair, for instance, the highest probability of success scenario is to pick up the computer and take it back to your shop for repair. If the customer "has" to watch you perform the work, then you need to decide if that customer is worth the hassle.

In my business, we capture this in a stated one-hour minimum, portal-to-portal. From the time I step through the door, our billable hours start. If we walk in, rectify the issue in 2 minutes and are back out the door, we bill for an hour. If it takes us an hour, our hourly rate is enough to cover the travel costs.

Ideally, you would not want to cover a huge geographical area like this, but I put a hard limit on customers being within a 20-mile radius of the office. It is rare that we get a request outside of those geographic confines, because we do not market outside of that. If we do, we charge from the time we leave until we either get back to the office or to the next job.

If you state it upfront, politely but firmly, no one should have a problem with it. Enforce the rule across the board, to everyone. If anyone expects you to come to them for free, you do not want them as a customer anyway.