I bought my first dinner jacket in St Andrews, where there were occasional "black tie" events. The decision came after I had borrowed one from a lecturer friend for an Edinburgh dinner and had to struggle through the evening in a dinner suit that was at least three sizes too large. Since I couldn't afford to buy a new one, I went to Fordyce's on Market Street (long gone) to view their ex-hire selection. They hired out dinner suits, and after several such hires they had recouped their investment and were happy to sell them off and replace them with new ones.
Since I was a fairly standard size, a ready-to-wear one presented no problem, and I found one whose jacket and trousers fitted me perfectly. It cost me £7, a very low price even in those days. It was good quality, though, and showed no signs of wear. It came with a plain matt black unpleated cummerbund.
Since black tie outfits look pretty much the same, students sometimes chose to express individuality by wearing coloured bow ties and cummerbunds, maybe in red or blue. In my case I asked a talented female student to embroider the plain cummerbund with a gold double-headed eagle spreading its wings across it. It looked spectacular, and started a minor trend as a few of my friends began to have theirs embroidered with different patterns.
It is a testament to its quality that I was still wearing the dinner suit 25 years later, and it still fitted. When I finally bought another one, it was from the "previously worn" department of Moss Bros – their euphemism for "second-hand" or ex-hire. I still have the embroidered cummerbund, and still wear it occasionally, but only at student functions since it would be out of place on more formal occasions.