Edifier R600USB
or
Edifier R600TC

or something smaller would be Edifier Prime M20USB

I don't know if it's under RM100 but I'd suggest these for small 2.0 setup
if you were to pick 2.1 I'd immediately suggests Edifier M1360 because it is super cheap that sounds expensive

Around RM100 and tight space, you could look for low budget speakers which are pretty small and mostly 2.0 (stereo) type such as Logitech Z150, Creative SBS A60, etc (and many more, including cap ayam brand ones). If you're willing to spend a little extra (more than RM100) then you may want to consider Edifier M2280 or Edifier M20 USB Hub...

There are more options/choices with 2.1 speaker systems in the mix...

Please note that these are small stereo speakers, thus do not expect them to sound/perform like a 2.1 speaker system or large stereo speaker systems especially when it comes to (very low frequency) bass. Check the frequency response graph below (source: Edifier.tw > Edifier Multimedia® > M2280). As always, try auditioning/testing them first (at the shops) before deciding...