Yes you can. I assume you already have a dataview with the Expenses entity. I assume you have a reference selector for selecting the Tool categories. You can then use a listen to datagrid to display the Tools. What I miss in your domain model is how you store which tool is bought. Furthermore I assume the perso can buy more then one tool at a time.
And can the person edit the Tools and Tool Categories? I would connect the Expenses with with Tools in a multiple - multiple relation. Because I think that a person can buy multipe tools and that those those can be bought by multiple persons. So in the dataview show a dropdown with the tools categories and show the tools belonging to that categories. With a (purchase) button connect that tool with the Expenses entity.
I suggest you follow the tutorial lessons again and search for some purchase order examples in the forum. I know there are a couple of topics in that area.
Hope this helps a bit.