Is the Sony PlayStation Wireless Stereo Headset 2.0 the best headset for that price? I'm looking for something with atleast 5.1.
Cheapest I can find is Amazon for £60.
If you're wanting 5.1, it most likely is, yes. Though, it only gives 5.1 on PS3/PS4. Other consoles and PC it will just output stereo, since the surround sound conversion is done by the console.
The better surround sound headsets(which isn't saying much because headsets in general have poor sound quality) are at least £100. More if you're wanting to use your own headphones, which will almost always have better sound quality than a headset. My setup would cost around £200, astro mixamp + Sennheiser HD 558's.