It's tough, but possible. Is there a major website/store you would buy from?
I live in the US and use newegg most of the time. For the uk I use overclockers.co.uk
Their selection isn't as big as newegg's so if you have a friend/family in the US then I'd suggest having them buy the parts and ship to you (yes, it will probably take longer, but should be cheaper - not always the case though.)
Anyway, overclockers.co.uk has a limited selection but heres what I'd pick up:
Processor:
AMD Athlon 64 X2 Dual Core 7750+ Black Edition 2.70GHz (Socket AM2+) - Retail
Motherboard:
Gigabyte GA-M720-US3 (Socket AM2+) PCI-Express DDR2 Motherboard
Memory:
GeIL Black Dragon Evo One 2GB (2x1GB) PC2-8500C5 1066MHz DDR2 Dual Channel
Video card:
Asus ATI Radeon 3450 Vcool Silent 256MB DDR2 TV-Out/DVI (PCI-Express) - Retail
You said that you want to be able to upgrade the CPU at a later time, well the motherboard will support AMD's Phenom X4 Processor (quad core)...I went with AMD because they seem to have motherboards that are compatible with a lot of their processors.
Note, the total is below what you asked for so you have a bit of wiggle room. Total: 157.21
That so shipping, etc. may push it up to 200, but if you were accounting for shipping costs already then I'd suggest getting a better video card for what I have above. (The one above should handle Guild Wars and UT just fine though)