Unfortunately, you are required to capitalize (treat as an asset rather than an expense) the toolbox, as well as any of the tools that cost more than $2,500 individually.
You may, however, be able to "expense" the cost of the toolbox by utilizing the section 179 provision. This provision allows you to, effectively, fully depreciate the cost of a long-lived asset that is considered personal property (not real estate).
Please note that section 179 cannot be used to generate a loss - any amount of section 179 claimed in excess of your profits will be carried over to potentially be used in future years.