A summary report based on the Item table with sub summary parts can produce report with totals for each category and either the same layout or a different layout can produce the same time of report grouped by location. This produces two separate reports, but other than that, it does exactly what you describe. The way to set up such a layout is with sub summary parts "when sorted by location" and "when sorted by category". Summary fields computing total number and total value can then be placed in the sub summary parts to produce sub totals.
If you do not want the report to list individual records and just show the sub totals, remove the body part from the layout.
Note that sub summary parts will not be visible in browse mode unless the records are sorted to include the "when sorted by" field specified for the sub summary part.