That depends on a number of factors.
What are you? A pat tester or a spark?
Sparks normally charge an hourly rate whereas pat's charge per item.
Where are you? Different parts of the country charge different rates.
Your client -if you have one client who has 60 items and another with 3000 your not going to offer the same price per item to both clients! Larger clients tend to receive discounts etc.
Personally my rates range from 75p - £2 per item subject to minimum charge.
I offer fuse, plug and flex replacements too aswel as microwave emissions testing.
Im not going into detail with my pricing structure for obvious reasons but this will give you a starting point.