4k to 5k, you can get 0.4 ct already from wah chan.
0.3x ct is still below your budget.

then just get the cheapest one possible.
vs1 and vs2 - for untrained eye, probably you need magnifying glass to see the flaw.
si1 and si2 - sometimes it depends on your luck, check it properly first.

but the colour h and g is not really colourless.
recommend to get d,e,f only if you want to put into white gold.

if you do not care about the gia cert, you can go to those shops in sg wang to compare the price, sometimes they are cheaper.
just that the diamonds there you do not really know if they are using d or e or f due to no cert.

I think i can get slightly cheaper than the price you get.. do you need my help to check?

do you have wahchan member card?
and do you have any contacts in wahchan?

additional 5 or 10 percent depending on item.