There are two ways you can get a report of the value of your inventory. The first is on the Dashboard page. Under "General Stats" click on the "Inventory" button. This will display the value of your inventory by retail (sell price x qty) or cost (buy price x qty).
If you want a full, broken down report of your whole inventory, you can export it on your Inventory > Products page.
All you need to do is under the "Variant Specific Info", set the filter for "Quantity between 1 and __". Then click "Export to csv".
You can then download the file from your Notifications > Generated Reports page. Open it in excel, and you can use formulas in excel to calculate the price x the qty for each item, and then total it up.
Can you get an inventory report from a specific date?
Currently, there is not a way to get an inventory report from a specific date in the past. When exporting your inventory, it can only export the current values. The inventory dashboard report can only display what the current inventory levels are. We don't have a way of reverse engineering all of the inventory changes to determine what the value was on a particular date in the past.
Because of this, if you are needing to get an inventory value for the end of the year, you will need to make sure you run your report on Dec 31 or Jan 1.