I built you one for about $290 including the case, psu, cpu, mobo, RAM, HDD, video card, DVD-RW/CD-RW combo drive, and I did shipping and handling out here to VA. All of this is on NewEgg.
Rosewill R103A Black Steel ATX Mid Tower Computer Case with 350W 20+4 pin connector Power Supply - Retail
ECS GeForce7050M-M (V2.0) AM2+/AM2 NVIDIA Geforce7050PV / nForce 630a Micro ATX AMD Motherboard - Retail
AMD Athlon 64 X2 4400+ Brisbane 2.3GHz Socket AM2 65W Dual-Core Processor Model ADO4400IAA5DO - OEM
G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-2GBNQ - Retail
Western Digital Caviar Black WD5001AALS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
LG 22X DVD±R DVD Burner Black SATA Model GH22NS30 - OEM
EVGA 256-P2-N429-LR GeForce 7200GS 256MB 64-bit GDDR2 PCI Express x16 Video Card - Retail
You won't need a fancy video card if your only doing video editing and really only need one for the dual display support. This card has one D-Sub, one DVI, and one S-video output. If your running two D-Sub monitor's the card come with a DVI to D-Sub adapter.
I looked all that up in about 5 minutes but it's more to give you an idea on how inexpensive building a system is. Putting it all together is really not as hard as you think it might be. There are plenty of written guides out there and I'm sure if you get on YouTube you could probably find a video.