I did some covert research in my area to find out what the competitors were charging. A Big company that starts with "O" was charging 220 setup plus 90 monthly. Now that includes bait stations/poison so consider that.
What I do is assuming the customer is in my home county I charge $175-200 for initial treatment including sealing up holes around the foundation and setting traps inside the house. Also built boxes to house snap traps outside the house like you mentioned. Then I leave it up to the customer if they want to monitor traps or have me come back and do it. If I come back, it would be $40-$70 per visit depending on size of property and ease of access (climbing on my stomach in a crawl space/attic for example). Consider your miles and time value for the return trips. mouse traps don't cost that much so I set it HEAVY to make sure they get caught. If the property is 20 min from home I figure 40 min drive time plus 20 min onsite checking traps etc, so I'm at about $70 for 1 hour of work not including expenses such as miles and trap maintenance. If your area can sustain higher service charge, do it. Some customers are terrified of mice and will happily pay for you to do it.