Its more expensive in the UK for some things as you have just found out. If you holiday in the UK like a lot of us, take advantage of being there to stock up on those things you can't get in the UK at a price you want to pay.
You have been living in the UK for quite a while but seem to be trying to apply US standards to your wants. Formal wear is not as popular in the UK, the cost of living is higher here which probably accounts for men being happy with less expensive suits. If you're happy to pay £400-£800 for a suit you should be able to get something made to measure. Asking at menswear hire shops might be an idea, they cater for all sizes and you might be able to get one made by their supplier.
Although your post came over as hostile I've tried to help you, perhaps your style of writing is just brusque!
Sounds like you offend easy, so I promise to be gentle.
From the top, let's begin. Yes, I have been living in the UK for quite some time, so paying exorbitant prices for abysmal quality and poor service is nothing new to me, but it doesn't mean I'll ever be comfortable with getting ripped-off on a daily basis. Then again, as the locals like to say, welcome to rip-off Britain.
I don't have any plans to holiday in the USA in the near future, so that option is closed to me.
You say formal wear is not as popular in the UK, and this confuses me. By the term 'formal wear' if you mean tuxedo or what they call evening dress on this side of the pond, then you may be right and you may be wrong. Nevertheless, 'formal wear' is not what I am looking to purchase. If by that term you mean just a regular men's suit then I disagree with your original premise. On the contrary, men wear suits far more often here than we do in the USA. Consequently, you would think that quality of the product would not be so unequal in what is available to consumers. Especially when you also consider that Britain is one of the largest wool producing nations on earth. That would make me think 100% wool suits would be everywhere and not so rare in the mid-price category, which in itself is almost non-existent. As my original piece said, the options for men's clothing in this country seem far more polarised to me, with few options in the middle. The only products available seem to be either very expensive, top-of-the-line luxury brands on one end of the spectrum, and cheap, mass-produced, ill-fitting, polyester rubbish on the other end. Finding middle-of-the-road priced, solidly constructed clothing made from 100% natural fabrics in Britain is next to impossible. And the few options available get even sparser the larger the size gets over 42, which in American parlance is only a medium.
You also infer that I can find a tailor to custom make me a suit for the same amount of money I am willing to pay (£400-£800) for an off-the-rack suit. If such a tailor exists in this country, I haven't found him. Bespoke suits start in the £1200 range, and £2000 is more representative of an average price (and they're even higher priced in London).
You also offer the idea of approaching a mens clothing for hire dealer. The only mens clothing for hire firms I'm familiar with are the ones who specialise in formal wear, eg. tuxedos, morning suits, evening dress, wedding attire, etc. I've never heard of any such firms who hire out regular everyday men's suits.
Now, as for your last comment, perhaps I did come off to you as being a bit brusque. I thought I was just being humourous in light of the amount of needless frustration I've been experiencing in trying to something as simple as just buying a suit. Then again, I know from personal experience that Americans often feel irritated whenever they have to purchase goods or services in this country, as the quality is often disappointing, and the service, while always polite, is usually lacking. Nevertheless, I am always mindful that the British (The English especially) are a proud people, who do not wish to be reminded they are no longer giants on the world's stage, and that their products are usually of a low quality - and certainly not worth the prices often charged. Consequently, Americans such as myself, who have lived here a long time come to learn to walk softly and reach for as much diplomacy as possible when forced to make large purchases. There's a certain default mode the Brits universally adopt in order to maintain their pride whenever they engage with Americans. It's the standard: 'Americans have no taste'....'Americans are all fat, stupid, loud and unsophisticated unlike us Brits'......'Americans don't understand quality or have any sense of understated elegance'....Blah, blah, blah. It gets pretty damn rich after awhile. The shame is many Yanks actually buy into those idiotic negative representations of themselves in their first few years living here. That is, until all the bad food, miserly economic practices, abysmal product quality, exploitative prices and lousy weather starts getting old.
You then come to realise its all a phony version of reality used by the British in order to keep up appearances. Ultimately, it really is just another game of rip-off Britain.