There is no such thing as MP5 - sometimes companies call 'generic' MP3 players 'MP4/5' as it often implies that there are other features offered, such as video playback and internet browsing alongside music playback.
There is not such thing as an MP5 player (nor is there a format called MP5). Generally players called 'MP5' are generic, cheap ones manufactured in China and are often modelled after more popular devices, such as PSPs, iPods etc.
Let me say this one last time: MP5 does not exist. If you want to save yourself some money in the short term feel free to go on a shady website and purchase one but it's not something which I would advise.
Remember - buying an officially licensed player, with support from the manufacturer and the seller will be worth the extra money if something goes wrong.
PS - Please don't post links to website selling this kind of thing or your IP will be blocked as spam advertising and you won't be able to post here any more.