Quote Originally Posted by UglyBear
............................Suit coats, for example. ............................ They actually look okay if you leave them unbuttoned, .............
No, no, UB! I am sorry, but suit coats, or suit jackets, when worn with a kilt tend to make you look deformed! They give far too much heavy emphasis to the upper body and, especially from behind, make you look "all body and no legs"! They are too long. They also restrict the swing of the pleats! A kilt jacket should be no longer than to the hip, or where the sewn-down part of the kilt's pleats finishes.

........ but then the Suit Purists will tell you that you should button at least one button.
Somehow, kilt jackets seldom look right when fastened, which is why, I think, we tend to have waistcoats which ARE fastened under them. Day wear jackets nowadays are usually worn unfastened and without a waistcoat - but a wide kilt belt IS worn. Tweed jackets AND tweed waistcoats are seldom seen worn together, but they were popular and 'correct' 70 years ago, much as waistcoats were 'correct' with tweed trouser suits or plusfours.

Maybe the only way to go truly formal is with a Prince Charlie jacket, but I'm interested in finding a lower-cost and flexible alternative.
The Prince Charlie is only one of several styles of formal, evening wear. There are Montrose doublets, Kenmore Doublets, Regulation jackets and vests, and Sherrifmuir jackets available from most Highland outfitters. Geoffrey (Tailor) has also very smart Mess jackets and GT Doublets.

To my mind, although I wear one, the Prince Charlie has become so much 'standard formal wear' that it is almost a uniform to be worn by all kilted men at formal events. In the same way that the ubiquitous Dinner Jacket (or Tux) has in trousered society. Let's try to break away from this restrictive style and show a little individuality! 8) My heart is set on a GT Doublet!

I regret I cannot help you with "a lower-cost and flexible alternative", although I've heard of some of your fellow countrymen buying up waiters' monkey jackets and having them altered! I hae me doots, however!