Button

I will give you a rough idea about how I did my pricing.

1/2 inch x 2 inch plate $2.75
1 inch x 2 inch $3.50

Includes engraving

50 cents more for each additional inch of material

contractors normally order large volumes so depending on the number, you can reduce the individual prices slightly.
As you can see the cost of material is extremely low compared to the price you would be charging.
Your first bet should be to get them to tell you what they are paying at present.
i hope this helps

Regards

Bachi