CPU Intel Core 2 Duo E6300 (1.86GHz)
Motherboard MS 7255
Memory 1GB DDR2 PC2-4200 (2 x 512MB)
Hard Drive 250GB SATA
CD Drive Dual layer DVD±RW
Video Card nVIDIA GeForce 7300SE PCI-E 64MB (up to 512MB with Turbocache)
TV Card Creatix Digital TV tuner (CTX948)
Sound Card VIA VT3310(UAA) integrated sound
Network Card VIA PCI 10/100 fast ethernet adapter
Modem Creatix CTX 609 SoftModem
Ports - Front 1x 6-in-1 Card Reader
2x USB 2.0
1x Headphone
1x Microphone
2x IEEE 1394 (FireWire)
1x Audio-in (left + right)
1x Composite Video in
1x S-Video in
Ports - Rear 1x PS/2 Keyboard
1x PS/2 Mouse
1x Parallel
1x Serial
1x IEEE 1394 (FireWire)
4x USB 2.0
1x LAN
6x Audio I/O
1x VGA
1x TV-out
1x Modem
1x TV Aerial
Keyboard Microsoft
Mouse Wireless Microsoft 3000 5 button mouse
Monitor LG Flatron L194WT-SF 19“ flatscreen
Printer Brother DCP-120C
Speakers Advent 2.1 surround with subwoofer
Webcam Logitech

What kind of computer is it? If you have a model number you can probably check the manufacture's website to see how much it costs. Or check bestbuy.com to see if there is a computer that is like yours.

Advent T9317

Is that a european computer? This site says it's about 600 Euros.Forums - PC World Advent T9317 or T9307? - PC Advisor (http://www.pcadvisor.co.uk/forums/index.cfm?action=showthread&threadid=269497&forumid=2)

Honestly, not a huge amount, few hundred absolute TOPS and that's due to the screen you are including.
Bear in mind Advent are PCWorld's entry level brand and not renowned for quality workmanship.

Have a look on eBay for some better ideas.