Source code includes the script and command file for Microsoft Windows: github.com/avinash311/QImportP.
The link can be used to view individual files and download entire package.
Quicken is a package that works pretty well, but the manufacturer has a tendency to periodically block functionality.
For example, Quicken 2006 has been unable to download updated stock prices since April 2009. Quicken 2006 itself installs on even the latest Windows 10 (2016) just fine. [As an aside, it is just amazing that Windows 10 has kept compatibility alive for old software – Quicken 2006, as well as the SendKeys method used by the script below! Kudos to Microsoft!]
There is certainly no technical decision to disable automatic stock price updates – it is just a marketing push, so make people upgrade even if they do not desire to move to a new version.
Quicken does have a manual “Import Prices” command seen when viewing the Portfolio. Therefore, it is not too hard to write a script that will download current prices, and import them into Quicken.
It is a .WSF file, a Windows Shell Scripting program. It has been tested to work on Windows XP, Windows Vista as well as Windows 10 (2016), and is available in source code form.
The script looks up current prices for a list of symbols, and stores the prices in the format Quicken needs. Optionally, it can automate the import of the prices in Quicken by using Windows automation SendKeys method.
May 2017: This script used to be able to lookup historical prices but as of this month, the Yahoo finance API no longer supports links to ichart.finance.yahoo.com. So /days:1 option (accepted by older versions of this script) will fail if the number of days is 1 or larger. Only /days:0 works, which uses a different API to download last known price only.
The source code which includes the script and command file for Microsoft Windows is here: github.com/avinash311/QImportP.
The link can be used to view individual files and download entire package: QImportP latest .zip
QImportP-0.6.0.zip [2015-04-09] QImportP-0.5.0.zip  (Older version download may be disabled by Chrome. Use Microsoft Edge browser, or use the source code link to browse older versions.)
Prices are looked up using the Yahoo Finance web site. Quicken manual import prices only accepts date and price for a symbol, it cannot import volume and other data.
The script does try to automate loading of the price data into Quicken, but the mechanism of using SendKeys is very fragile, it may not always work – keys may get to the wrong window, or at the wrong time.
Version 0.3 of this package added support for non-US users, based on the code given in a comment (#5535), the /dmy and /div100 options provide that support. From what has been reported elsewhere on the web, shares and mutual fund price downloads in UK are priced differently – shares in pence, funds in pounds (or vice-versa?). So QImportP provides the /div100 option which can be used when needed.
The QImportP package is placed into Public Domain.[The original post with all old comments here: Archived Import Prices Script – 2009-2013]