In episode 2 of UFC Primetime GSP vs Hendricks, GSP says he bought an octagon and that it cost a consiferable sum of money. Anyone know how much it costs to buy one?
Good question, in. 
UFC octagon is 30'
Title MMA competition 30' octagon is $15,999
They talk about it in this video:
http://www.youtube.com/watch?feature=player_detailpage&v=JUyLm3etLvI#t=19
Need a blue to embed.
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MrFluffyHippo - UFC octagon is 30'Doubt gsp paid that kind of money, he probably got a hook up for Dana or Lorenzo
Title MMA competition 30' octagon is $15,999
I believe the UFC make their own cage so there isn't a price for a "UFC Cage." But companies like Throwdown and Revgear have their own cages that are probably not too far off in quality. Revgear's 30' cage is $22,000 and I would think Throwdown's would also be in the $20-25k range. There are cheaper ones out there, I think Monster has 30' cages for about $12k. Throwdown by the way makes the cages for the UFC Gym so they are quality.
Time lapse of a Throwdown cage at UFC Gym
https://www.youtube.com/watch?v=bZVOOakZg78
Considering the amount of money he pulls for the UFC, they should have given one to him for free.
UFC gave it to Tri-Star. It's a patented design/patent pending surface, can't just go buy one on Amazon.