I've run into a glitch where I seem unable to buy the Alchemy lab for Breezehome in Whiterun. I've spent the 500 gold several times, yet it never disappears from the Steward's menu, and the upgrade never appears in my house. I'm on the XBox 360, so console commands can't help me.

And your sure you bought it? saw the "500 gold removed" appear on the top left of your screen? And you selected buy and not "no more decorations at this time" selection?