Things I would include in client cost besides straight out of pocket expenses:
- Mileage. Standard practice includes enough to cover wear and tear and insurance on your vehicle. You may have already factored that in, but just in case...
- Whatever percentage of your cell phone or business phone bill that gets used to make sales calls every month.
- SEO, if you use it. Web hosting costs, percentage of internet costs.
- Cost of industry publications, if they include advice on getting or keeping clients.
- Software used to keep track of and communicate with clients, ie, if you have a CRM (customer relationship management) program of any kind that would be included.
For the time, I'd use my regular hourly rate. This is why - I believe you are supposed to use your "opportunity cost" for this sort of thing. Since no one is ever going to pay you to drum up business for yourself, trying to figure out what a reasonable "going rate" for your time spent acquiring clients is kind of meaningless. Yes, you may not have enough business now to have to make a choice to forgo paying work to spend that time finding clients, but hopefully some day you will, and when that day comes you need to be able to compare apples with apples in order to have a meaningful analysis of your business costs over time.
Edited to add: You are probably already doing this, but... when it comes time to calculate how much getting clients is costing you, don't forget to add in your time and money spent that did NOT result in getting a particular client. Ie, take the total number of hours spent on client acquisition, divide by number of clients acquired during that time. That's your real cost. Keeping track of what it costs you to obtain a particular client may also be helpful in deciding whether to keep them or not, or whether to try to find another client like them or not, but that's another subject.