Service Part Price Calculator is a handy little widget I wrote for calculating prices of Apple's service parts. It works with the XLS file you can download from GSX after which it will work without an internet connection. It's especially useful since GSX has been so incredibly slow for quite a while now.
It's really simple to use - just download the pricelist from GSX (Parts Lookup > Download Complete Service Parts Price List) and unzip. Then drag the file onto the widget (just grab it and enter Dashboard). Flip the widget to set your VAT, margin, shipping costs and currency exchange rate (enter 1 if your currency's the same as in the file).
Then just use the search field to filter the parts for the selected product. The search field filters all the visible columns. Vintage parts are excluded from the datafile upon import. You can also use regular expressions as a search term. :-)
The price calculation formula doesn't add margin to the shipping cost, check main.js at around line 207 to tweak it to your specific needs.