Why not just buy off the shelf vehicles like other posts or courier companies? Like Volkswagen Transporter, Mercedes Sprinter or Ford Transit if you want American
The USPS has a bunch of highly-specific requirements that they aren't willing to change, which makes an off-the-shelf van impossible.
These are things like: giant unpainted bumpers, sliding drivers door, the rear door has to be roll-up rather than normal doors, step through from front to rear, some size requirements.
One of the alternatives which was rejected when they signed the contract for the new vans was a customised Ford Transit.
You can get really decent pair of stable boots that can last many years for pretty reasonable price. The increase in quality compared to price of some super custom boots isn't actually sensable.
99% of what rich people buy is not of some massively superior quality. Specially in terms of clothing.
Maybe some really good winter clothing is a exception, but even then layering is probably a better solution to stay warm.
So really I don't buy this explanation unless people can give me some better examples.
There's always a point of diminishing returns, but it doesn't really make much odds where that is if you've not got the money. If you've only got £20, it doesn't really matter that good long lasting boots can be bought for £50 not £300.