Hmm, really depends how heavy is the 18k white gold your vendor is providing. And what are the contents.
For example, 18k white gold with palladium is more expensive than 18k white gold with nickel.
Assuming you are getting 18k white gold with nickel, 3.3 - 3.6 gram (according to Memory Jewellery), a default design in their inventory will probably cost you some price around RM 750.00 (last check on 7 Feb), while for custom design, the price will vary, probably around RM 1000 - RM 1500. Best if you reach out to them and check things out.
This 0.33ct E VS2 WhiteFlash diamond [
https://www.whiteflash.com/loose-diamonds/r...id=myengringexp (affiliate link)] is bigger than the 0.3ct offered to you, and has better proportions. M2U for Forex rate for transfer now is 4.461. Therefore, the final price for this loose diamond is RM 3974.75. Add 6% GST will be around RM 4213.24. Add on RM 50 misc. charges for things like GST on freight, M2U TT transfer charges, final price will be RM 4263.24.
You can probably get this ring set in your default/custom design with a final price between RM 5013.24 - RM 5763.24.
Also, if you get a loose stone and ring setting from the same vendor, usually the ring setting price will be cheaper compare to what you can get elsewhere. So, if I assume the price of the ring setting that is offered to you is at RM 750, this make the stone to be around RM 41xx. In this case, then I don't think the stone is worth it, given the fact that it has a crown angle there is over-steep and a medium fluroescence.
Hope this helps.