Defo don't go super cheap if you can afford not to. I'd look at places that specialise in formal clothing like TM Lewin (if you can find a physical store, as they've gone pretty much online exclusively), Charles Tyrwitt (never bought a suit from them but have a few overcoats which have been decent) or Moss Bros. Boss is my personal choice for suits, mainly because they fit me pretty well off the peg which is definitely not the case with most places. That brings me to the most important point - any suit will look rubbish if it doesn't fit well. A good shop will help you with fitting and offer alterations. If hiring then the shop will do all the fitting anyway.