Reason for RS,Anthem,BAS and maybe Sondi to be cheap is that you can visit factory yourself and pick your bat from scratch. There are so many less known/heard names that I haven't mentioned.
BDM don't make bats for any brand so they stand own their own with own price tags.
In my head, UK brands with bats made in India are still expensive due to taxes in UK. Shop rents,business rates import duties etc. There are many other things involved that rise cost and they have to make living out of it.