Ok, Custom Bats are 9/10 better because they are handcrafted as opposed to mackine made or mass produced in India, you can literally have the bat customised for you so that it suits your requirements, it is made in England so helps the economy.
Of the three bats you mentioned go for the GM option as they are made in England as opposed to India, Salix and Newbery are absolutely top notch and you can't go wrong, Bradbury however are predominantly Indian made now.
And yes you can get a Grade 1 custom made bat for under £160, I would reccomend Solitaire cricket for £100, Hell4Leather for £??? or Redback for £180ish but its above your budget slightly, worth it though!
Hope this helps mate and if you have any more questions please ask.