Sorry this got long, total brain-data dump here.
John T. Malloy (yes the Dress for Success author) has good tips on wardrobes and shopping. He advises that you go and try on the exact same thing at a high end store (really high end), a really low end store, and one somewhere in the middle. Look at the insides and the construction, how are they put together? You will start to see the things that go into higher end clothing - better seams, better fit, etc. Slight differences (or glaring differences) in the dye job*.
Then you can recognize the few items that are less expensive but look like quality.
If I remember correctly he also discusses which flaws are easily corrected by a tailor (hem and sleeve length) and which are not, so you don't buy something thinking that a tailor can fix it, and the tailor can't.
Believe me (my DS and BIL both had high-powered jobs and spent a small fortune on suits) the higher-ups will generally be able to judge how expensive your new look was. So you want it to be perfect/look expensive even if it wasn't expensive. The higher you go the more this is true. So in this regard, buying quality second-hand is better than buying cheap new, if the second-hand is still in good shape. Just don't get anything obviously out of fashion - and yes, there is men's fashion, just more subtle than women's fashion. And this is why you do the high-end scouting trip every time you are planning a major purchase, so you look up-to-date. If you have access to one-day factory sales at high-quality manufacturers, go to them. I had a wonderful Aquascutum raincoat, factory one-day sale at the Montreal plant. These are not generally advertised, they are word of mouth. Sometimes foreign tailors have days when they are in a city, take all your measurements, show you styles and fabric, and then go back to their own country to do the manufacturing - and a few months later you have a perfect fit wardrobe. DS and BIL used to do that, great clothes, not cheap, but less than North America.
If you have a colleague who always looks well dressed and you know they are not blowing a fortune on clothes, ask them for advice. This assumes you like each other and are not in direct competition, of course ;-)
General thought - my teaching wardrobe (biologist -> labs) was decent but casual. I had a few much higher-end outfits for when I had to make presentations at higher levels, including to our board of directors. I still looked like an academic, not a businessperson, but a much more professional academic. So anyone who might ever have to meet (occasionally or often) with people levels above them should have the clothes for those meetings. It gives you credibility.
*Primary colours are considered lower-class for a historical reason, they were cheap and the dyes held well. It is hard to get subtle muted colours in a dye job, so those fabrics cost more. Beige/tan raincoats need cleaning more often than black ones, so if you are on a tight budget, you buy black.
