If you look on their website they do have a price grid. What would be helpful if they give cloth examples.
They are currently making me two mtm trousers, Minnis 16oz flannel and H&S crispaire. Their mtm trousers start at £190 but mine cost £280.
Bicester Village - yes
Westfield - just go into central London instead
If you do not find anything at Bicester Village; walk down Jermyn Street, you will have options like TM Lewin that are within your budget - if no luck, Marks & Spencers on Oxford Street (near Selfridges)