There was an error in the Mac App Store. Please try again later. (13)
I was experiencing the same problem: unable to purchase or update any items from the App Store, with an error code (13).

I came across another thread here - Cannot Install or Update Apps in App Store - Error 13 app-store-error-13 - which basically suggests deleting a cookie-preferences file for the App Store. I tried it, and it indeed worked for me.

The steps are:

1) quit the App Store app, if it's open.

2) delete the file, which will be in: ~/Library/Cookies/com.apple.appstore.plist

3) restart the App Store app, and try purchasing or downloading/updating something.

Let us know if this fixes the problem for you! :-)