I know CPL used to do this (I dunno if it still does), where they gave you the base package and provided some upgrade options.
Does UMART allow such a thing? Not to mention do any other computer stores offer such schemes? I ask because my parents are adamant on having a warranty for any new PC (planning to get one soon), yet I'd still like something better than base computer packages being offered (such as adding an SSD or switching the graphics card).
Umart (when I emailed them in April) does not allow you to upgrade/modify their packages. (Apparently they are already at the best price.) However, you can request a quote for the system you want, just copy paste the same parts with your modifications. The price they gave me at the time was not the best quote I got, though. ($874 before shipping; I ended up getting it for $850 with shipping with Maco Technology; probably not of interest to you, though, since free shipping only for Syd. XD)
What's wrong with CPL..? Just curious.
Other companies that will respond to quotes: NSCom, D&D Computers, Eyo (will put it in the trolley for you, lol), PCMarket (sounded nice but wanted to charge me $1380..), Maximum PCs, and PCDIY.
Maximum PCs (http://www.maximumpcsau.com/) actually quoted me $850 too; but the system wasn't for me, and my parents decided to go with the company with more reviews on Whirlpool. A pity. Great customer service trying to help with my builds. Sorry, Alfred!
Mwave has upgrade options on their site but it always seems overpriced to me. PCCG will suggest their own systems instead of giving a quote. And they'll suggest systems that 'do not include SSDs as they are unable to fit in with your current budget.' Lol.