The last price was updated around 4 months ago. Here's the new suggested price. Not many are on the market (~4). I personally bought one for 1 bud.

Proof:

1. http://www.tf2outpost.com/trade/8490573 - Received offer to upgrade to orbiting planet (around 1.2-1.3) one if the player adds 6 keys + the bubble.

2. http://www.tf2outpost.com/trade/8504187 - Selling @ 1.5 but received counteroffer @ 1. Re-offered 1.3 and is currently being considered.