Using order entry to track job costs


We've often wanted to find a way to track our job costs in Sage, but have struggled to find a built in way to do so without purchasing additional modules or 3rd party software. Recently, we had the idea that we could make an item category such as "Internal", and then create part numbers such as "Hotel Cost", "Labour Cost", "Travel Cost" that use the "Internal" category.   Then we would add these to orders as separate line items with no selling price and specify the costs.  We wouldn't show items set up with the "Internal" category on customer facing documents such as invoices or order confirmations.   Depending on the success of this, we would look to track more things like "Vehicle X"  to track depreciation and usage of Vehicle X, or "Labour - Employee Name" to track usage of employees, etc. Does this seem like an effective way of tracking costs associated with an order?  Is there any potential problems that we may not have anticipated? Is there better options? 

Thanks for any advice..