How to unlock Lumia 520 for Free/cheapest

Hi I got a locked lumia 520 from UK the set is locked and I can't use local sims on it, I checked the market and they are demanding 2000-2500 (thats the actual price of used 520 set) I need to know some cheap or free solution, or a way to install some App like youtube or games so I can give it to my daughter for watching cartoons.

Try "unlockbase" website. They sell cheap codes and are reliable aswell because recently I have ordered a code for my Sony Xperia in 6$ for which the local shopkeeper is demanding 2800 pkr

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locked on what mobile network?