Autocad & 3dsmax don't have Quadro optimizations as far as I am aware due to being DirectX.
TITAN RTX as baseline:
" Autodesk's AutoCAD is now almost a standard DirectX application, both in 2D design and shading in 3D views. "
"The 3D result is dominated again by Nvidia and everything is grouped as one would expect from a computer game and DirectX11 that is not exactly dead-optimized. But here, too, the differences can be measured and displayed in the bars, but are hardly noticeable in daily use."
Really I wouldn't look lower than 8GB GDDR6 VRAM so RTX 2070 Super (TU104 similar to RTX 2080) is a good bet at $500 for price/perf, it's the gamer version of $1000 RTX 4000 (TU104) with improved CUDA count. Could probably undervolt it and use Nvidia's Creator driver (not Quadro driver). Less than that there's the RTX 2070 / RTX 2060 Super 8GB but those are ~$400.
On Quadros the best you'll get for $500 is P2200 which is Pascal based GTX 1060 5GB GDDR5X.