As Mark says, it depends entirely on what you want from the machine; R5 for instance, can support 3D Blu-ray etc, then there are features such as BDLive etc, that some may wish to look for, then streaming/internet capabilities on some models, the more you pay, the better the player/recorder, but that does not always equal to better value-for-money (are the features of the £200 worth £120 more than the £80 machine, to you, for instance?).
If you just want a bog-standard blu-ray player, most will do just fine, though ideally, a 2010 released model or later is a better choice for compatibility reasons - most players in the shops etc will be 2010 onwards, however some of the cheaper models (even big-brands as well as small brands) may be older models rebranded, or just refurbished/surplus stock etc, so its always worth checking on google, when the model was released. The earliest players from the likes of Philips and Panasonic, are known to have some serious issues with compatibility as they are earlier revisions of the technology/bleeding edge product releases.
A decent option, if you just want a player, but want the ability to add-on further services such as streaming tv etc, may actually be a PS3, if you can get one cheap enough!!