I have a lot of suits, more than i need for the line of work I'm in, because I love them, how they're made, and the quality of a fully canvased, hand finished, well tailored suit is a thing of beauty. I have never paid more that $1000 for a suit, but that's because I'm extremely careful on what I buy, from where, and for how much, but some of my suits would retail for $4k. You do get what you pay for, but expensive does not necessarily equal quality.
My advice on those new to suit buying is as follows:
1. Fit is the most important element in a suit ... which leads to:
2. Get to know your tailor. A good tailor is more than someone who shortens pants hems ... they can adjust nearly element of a suit so that it fits you as it should. In this, you will REALLY get what you pay for, so read online reviews critically and find someone who knows how to deal with tailored clothing. I've paid as much as $200 to have a jacket adjusted, but they practically took it apart and put it back together ... his rates were high, but the seamstress in the corner of your local dry cleaner could NOT have helped.
3. Fit is most important, but particularly in the shoulders ... this is the aspect you need to nail and by far the most difficult to alter after the fact. Do not get something too big, everything will hang wrong and you'll look like you're wearing your dad's clothes. Do not get something too small, the suit will pull, be uncomfortable and the seams will be the worse for it. Try on lots of jackets, figure out what is truly too small, as a well-fitted suit can feel snug the first time you wear it, but your perceptions adjust.
4. Buy off the rack unless you're very oddly proportioned. Different labels will cut for different shapes, so figure out "who" fits you. If you want to go a bit custom, do investigate Suit Supply, they have pretty good quality for made-to-measure (which is not a custom bespoke suit).
5. Your first suit should either be a medium/dark blue or a medium/charcoal gray ... get one of each. No stripes or plaids as you build your suit wardrobe ... they are more formal and less versatile. Stripes and plaids are ALWAYS on sale ... stay strong.
6. Try to stay with 100% wool, for durability and longevity. Worsted wool or super 100's will be more durable than super 120's or higher.
7. Quality of suits varies highly and mass retailers (Macy's), tend to carry the lowest quality examples. You can get a gorgeous, fully canvased super 120's suit by Eidos for $500 or less if you shop online from someplace like SaksOff5th ... you can spend $500 for a garbage Calvin Klein white label at Macy's. I actually like the quality of stuff at Banana Republic ... much higher quality than you would expect for the price point, and their shirts are pretty good too.