This article explains the price for Real-Time Quotes, which includes MarketTracker.

With the Real-Time Package, you can see live quotes on the Yahoo! MarketTracker and across the Yahoo! network, including Yahoo! Finance and My Yahoo!.

The Real-Time Quotes package costs $13.95 per month when billed monthly, or $131.40 ($10.95 per Month) when billed annually. It will be billed to the credit card you provide as part of Yahoo! Wallet registration and is non-refundable. To register, go to the sign-up page.