If you are looking for value for money, you should tell the sales person you are looking for GIA diamond. The last when I surveyed, their GIA diamond is priced very competitively. 0.3 carat, you can get your whole ring ard 3.5k. I think you can also check their gia prices in their website.
That's why you need to know what you want. Do you want bigger size or do you want better quality?
But no harm comparing prices around. You should always survey/research different jewellers for prices and quality before settling on your diamond ring. The after sale service is also very important.
But in real life, you can find similar or a diamond that can show their cut quality in a more transparent way from other vendors.
You did not mention the other specs other than the 4Cs. But nonetheless, even if it is an overkill D colour Flawless clarity, it will still be overpriced.
You can consider it if brand name is something you are looking for. If what you are looking for is just diamond, other generic jewellers will offer you better value for money.
Personally, I will be more interested in a brand if the brand offers something exclusive to their brand name, for example the Decagon cut from JannPaul. Or some very exclusive jewellery design a brand has.
at the end ive gotten 0.50ct H/SI1 for rm6.5k from Zcova
not sure if it's a good deal but the ring design is very nice and unique