My guess is a."good" off the shelf "gaming" desktop, from fry's or best buy, with 8 or 12 ram, and nVidia graphics card might start at $800.. "great" for $1000... "screaming" for $1250... just guessing... but generally I would search for ,"gaming" rigs, as the game requirement specs are similar to 3D architectural modeling requirement specs...
Thomas, found this for about $800, might this work?
Processor
4th Generation Intel® Core™ i5-4460 Processor (6MB Cache, up to 3.4GHz)
Operating System
Windows 8.1 (64Bit) English
Memory
8GB Dual Channel DDR3 1600Mhz
Video Graphics
NVIDIA® GeForce® GTX 745 with 4GB DDR3
Hard Drive
1TB SATA 6Gb/s (7,200RPM) 64MB Cache
Multimedia Drive
Slot-Loading Dual Layer Blu-ray Reader (9.5mm)
Media Card Reader
No Media Card Reader, includes USB 3.0
Bluetooth
Bluetooth® tied to wireless card
Display
No Monitor
Fax/Data Modem
HDMI - Yes
Wireless Connectivity
DW 1506 802.11 b/g/n Wi-Fi
Audio
Internal High-Definition 7.1 Performance Audio with Waves MaxxAudio®