Building it yourself isn't a major concern (you can always get help online if something confuses you).
One big advantage of custom builds is the NVmE storage cards (M.2 card format) that are 100 times faster than SSDs and 1000 times faster than spinner drives. Get a motherboard that supports one and install your OS and applications there. You'll get faster boot times. I have spinners for data (not as fast, but I need terabyte memory and that's still very expensive in solid-state storage).
I assembled my system (see my tag line below) in the $1,500 range. Just be careful of the NVidia graphics cards that advertise built-in 3D processing (Real Time Ray Tracing aka RTX) because TurboCAD doesn't access those capabilities, so you will be wasting your money unless you buy some computer games that use it. The Quadro cards should increase rendering performance, but I don't know how much. You can find a wide variety on https://pcpartpicker.com/
(a search for "Quadro" will result in 3 pages of results), but you'll have to do some research to determine which cards will do the best job for you.
Pick the power supply last, because it has to drive everything.
Some of the Quadro cards are well under $1,000 (but you'll want a minimum of 3GB, probably 4), so you can build a quality system for well under your $2,400 maximum price.
TC Pro Platinum 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1