SixthSandwich,
Somethings depend on what you mean by AutoCad- strictly 2D or 3D with rendering, photoediting. Generally, I'd say that within that budget, I'd buy a used dell Precision T3500 with a quad core Xeon CPU of 3GHz or more (about $150-200), add RAM to have at least 8GB, a graphics card- something like an AMD Firepro V4900 or Quadro 2000 / 4000, and a 1TB Western Digital Blue HD. The older Quadros (e.g. FX 3800) are very good in 2D if your work is only 2D, but really any image-making system today should have some good 3D capability. Some of these used systems will need the OS, for which I recommend Windows 7 Professional 64-bit.
For a monitor, buy a 24"- or 27" if you can, looking at Samsung, ASUS, and Viewsonic and see the monitor in person before choosing. If you can find a generic/budget brand 27" within your budget that you like, it may be worth it to have the larger screen- saves panning and zooming, plenty of room for menus.
It's possible to have a good performing and reliable system within your budget but a good deal will requir careful and d patient shopping. When looking at used workstations, googlize the manual PDF and check the CPU ratings here:
http://www.cpubenchmark.net/cpu_list.php
And, when choosing a graphics card, look at the Autodesk list of recommended and certified:
http://usa.autodesk.com/adsk/servlet/syscert?siteID=123112&id=18844534&results=1&stype=graphic&product_group=12&release=2014&os=32768&manuf=all&opt=2
It's possible to build a new system within that budget, with good performance, but without much left for a monitor :
BambiBoom PixelPusher GrapharificBlaze iWorkPlay 8000 $®©™£?^(SM)©_$800_REV 2.14.14
1. AMD FX-6300 Vishera 3.5GHz (4.1GHz Turbo) Socket AM3+ 95W Six-Core Desktop Processor FD6300WMHKBOX > $120
2. Cooler Master Hyper 101i - CPU Cooler with Dual Direct Contact Heatpipes - AMD Version > $15
3. GIGABYTE GA-970A-DS3P AM3+ AMD 970 SATA 6Gb/s USB 3.0 ATX AMD Motherboard > $85
4. 8GB Kingston HyperX Blu 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model KHX1600C9D3B1K2/8GX > $57
5. AMD 100-505637(100-505860) FirePro V3900 1GB DDR3 PCI Express 2.1 x16 HDCP Ready Workstation Video Card > $115
6. WD Blue 1 TB Desktop Hard Drive: 3.5 Inch, 7200 RPM, SATA 6 Gb/s, 64 MB Cache - WD10EZEX > $65
7. CORSAIR CXM series CX500M 500W ATX12V v2.3 SLI Ready CrossFire Ready 80 PLUS BRONZE Certified Modular Active PFC Power Supply> $60
8. SAMSUNG DVD Burner 24X DVD+R 8X DVD+RW 8X DVD+R DL 24X DVD-R 6X DVD-RW 16X DVD-ROM 48X CD-R 24X CD-RW 48X CD-ROM SATA Model SH-224DB/BEBE - OEM > $20
9. Antec Three Hundred Black Steel ATX Mid Tower Computer Case > $55
10. Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) >$85
_____________________________________________________________________
TOTAL = $677.
> and building does require researching, ordering, assembling, configuring, testing, and troubleshooting.
Cheers,
BambiBoom
HP z420 (2014) > Xeon E5-1620 quad core @ 3.6 / 3.8GHz > 24GB ECC 1600 RAM > Quadro 4000 (2GB)> Samsung 840 SSD 250GB /Western Digital Black WD1003FZEX 1TB> M-Audio 192 sound card > AE3000 USB WiFi > HP 2711X, 27" 1920 X 1080 > Windows 7 Ultimate 64 >[Passmark system rating = 3923, 2D= 839 / 3D=2048]
Dell Precision T5400 (2008) > 2X Xeon X5460 quad core @3.16GHz > 16GB ECC 667> Quadro FX 4800 (1.5GB) > WD RE4 500GB / Seagate Barracuda 500GB > M-Audio 2496 Sound Card / Linksys 600N WiFi > Windows 7 Ultimate 64-bit >[Passmark system rating = 1859, CPU = 8528 / 2D= 512 / 3D=1097]
2D, 3D CAD, Image Processing, Rendering, Text > Architecture, industrial design, graphic design, written projects