First of all you need to get your ps3 downgraded to version 3.55 or lower you can check if your ps3 is downgradable to this firmware or not by using [ Register or Signin to view external links. ] you will need to check the serial number on the back of your ps3.

You can check if your ps3 is downgradable or not also by using a tool called minimum version checker use this tutourial to help you [ Register or Signin to view external links. ]

If your console is downgradable then you can purchase a downgrade off ebay or gumtree

If your ps3 isn't downgradable then the only thing you can do is buy a pre jailbroken one.

If you have a ps3 on 3.55 firmware you can use this tutorial to jailbreak it [ Register or Signin to view external links. ]

You first need to downgrade your PS3, you can do this by buying a E3 Flasher. Youtube has some good tutorials on how to use the E3 flasher to downgrade. Once you have downgraded you can jailbreak your PS3.

Id suggest just buying a Jailbroken PS3; Its much quicker and easier. Take a look in the PS3 marketplace on this site, there are many people selling their Jailbroken ps3's.