Haven't played it myself, but a few mates really got into this.
Next cheapest is about $30.
Critic and user reviews are around 7 out of 10.
Link to PS3:
http://www.zavvi.com/games/platforms/ps3/brink/10072699.html
Edit: Thanks to Puff Braddy for pointing out free DLC just released for this game
"Agents of Change: The first DLC for Brink, released on 3rd August 2011 for the XBOX via XBox Live and 4th August 2011 for the Playstation 3. The Agents of Change DLC will cost nothing on all platforms for the first two weeks of release to stimulate more players into the online servers, however after the first two weeks the DLC will cost $9.99 USD to download.
The pack contains additional content for the game, including new maps, abilities, attachments for weapons, and clothing and also raise the level cap from 20 to 24."
For PC if you have tried the free weekend. I found some local servers still peoples playing but not very sure just because of the free weekend or not.
Mainly MP game if not many playing there is no point to buy it.