I generally buy bikes used because there are always excellent, very-low-miles bikes where somebody else took the depreciation hit for whatever reason.
The most I have ever spent was on my current road bike - 2016 Wilier GTR SL with Ultegra 6800.
I paid $1,600 from the Pro’s Closet consignment. I don’t think the bike ever saw a real road. Was spotless and way below $3,500 MSRP.