I'm sorry, I just have to address this.....
In addition to being a bassist, I've spent my professional career working in the financial services industry.....I'm one of those "office nerd middle management wannabes" you deride above. For the last twenty years I've been expected to dress professionally, and I've been fortunate enough to find enough success to be able to afford quality clothes. In addition, my professional attire gets quite a workout, given that I wear it 9+ hours a day, five days a week. With that as background....
You seem to be asserting that a $75 suit (including shirt and tie), with proper tailoring, can't be discerned from a quality suit unless one compares the labels within. I can promise you that this isn't even remotely true. From the fabric, to the fused collar, to the fit and ability to be tailored, there is a massive difference. While you may be unable to see a difference, I promise you that anyone with a more sosphificated eye can tell in about 2 seconds when they see a suit that cheap. And while at some point you may be "buying the label", I promise you that breaking point isn't $75.....
Now, can one buy a $75 suit and make it work in a corporate band environment? Sure, within limitations. A super cheap suit will lack durability, so it will take limited laundering and withstand less abuse than properly made clothing. Because of the construction methods of those suits, specific altering can be complicated, and dramatically more expensive....usually prohibitively so. I'm not talking sleeves and pant legs, I'm talking jacket and shirt waist, pant seat, etc. If one can find a suit in this price range that fits decently in the seat and waist, then the rest can be handled by a tailor (and will double the cost of the suit. ). But be assured that it will look cheap to those who know, but that rarely matter to bandmates in these situations.
For a more realistic budget of about $250 (excluding shoes), a "smart shopper" can cruise the sales and find a much better quality suit that will not only look nicer and wear better, but will take seriously altering for a proper fit. Expect alterations to cost an additional $100 or more, depending on your build and alterations needed (jacket alterations tend to get expensive.)