how much does it cost to get the latest version of safari

Nothing. However, you need to update your OS. Open the App Store and search for OS X Yosemite, and install it.

The latest version of Safari, 8.0, requires Yosemite, 10.10. An Early 2011 MacBook Pro will run Yosemite very nicely...that is what I am using for this response.

Yosemite is a free download from the Mac App Store, just search for Yosemite and you will link to the download.

What everyone is trying to tell you is that Apple doesn't offer Safari as a separate downloadable and upgradeable app.

Apple forces you to upgrade or update your entire OS X system to get an upgraded/updated Safari web browser.

If you rather not have to upgrade your entire OS X system to get just a Safari web browser upgrade/update, do a search for and look at, download and try

Mozilla FireFox, instead.

Mozilla FireFox web browser is a stand alone, Mac-friendly web browser that gets continual updates without having to upgrade/update your entire OS X system.

Good Luck!

What MichelPM suggested is the SAFEST solution. Firefox is a better browser than Safari, and you will not be faced with any potentially crippling consequences of a full OS update.

You will presumably have to update your system at some point, and you should prepare for that by maintaining a full, up-to-date backup of your current main system on an external hard drive. You can use SuperDuper ($25) or Carbon Copy Cloner (the legacy version, 3.5.7) to clone your current system to an external drive. This drive will be bootable and will provide you will a safety net if you decide to install Yosemite at some point.

Firefox