Hi Island,
Now it is actually quite cheap to get a DIY PC from Sim Lim. However, you'll need to have a bit of knowledge regarding what are the good hardwares to get. The installation fee is about $40, some may be free if you buy all the hardware from the same shop.
If you don't mind using AMD microprocessor, it is possible to have a computer at about $1000. Just add about $280 for a 17" monitor.
Regards,
Chin Leng.