What would be the estimate cost for:
Carat - 0.3 to 0.4
Clarity - VS2, SI1
Colour - H, I, J
Cut - Excellent

And have anyone out there proposed before with other than diamonds - e.g. Ruby, Sapphire, Emerald etc? 

Nope, with the same amount of money, can get F colour and IF clarity, or E colour VVS1.

Say earlier lar.  Diamond for RM 3.1k is about there, for GIA certified diamond.  Can get a bit cheaper, but judging from the price you're paying for the setting, I wouldn't recommend getting it elsewhere as the price difference will be only a couple of hunderd.

What is the GIA number of the diamond?

Like I said, get the GIA number.  Without it,  hard to make a call.

And which shop is it?

Personally don't think I will get 0.34crt H SI2 Triple Excellent. Based on specs alone, 0.30ct E VS2 with ring from Tailored Jewel only cost RM 4,400. RM 300 difference for a colour that is 3 grades higher and clarity that is 2 grades higher is good for me. 0.34ct and 0.30ct size difference is too minimal to be noticed.

Which one is worth? I will go for 0.25ct, if compared between the two you have.

Based on specs alone? No GIA number provided? Will get 0.25ct. Side diamonds can probably make you stone look bigger too. As far as I can tell, you main concern is budget, so I guess 0.25ct can fall comfortably within your budget too. Besides, the price is quite reasonable. Anyway, if you have the time, just go to a diamond shop to survey and look see. Places like Wah Chan is pretty budget friendly from what I've heard. Try to get the GIA cert number for the diamonds that offer.

There is really no noob question btw. Most guys will have to go through this. Haha... wait, you are a female?!

First of all, diamonds are the same throughout commercialize/non-commercialize. If you buy from Wah Chan or buy from non-commercialize stores, like Tailored Jewel, they all have a GIA cert. So, give yourself some flexibility to explore various shops. Just my opinion.

I always prefer diamonds mounted in simple 18-K WG setting.

Actually, what is your main concern when making a purchase?

Last check with Eumayco is that you can view the stone before making a purchase (because I asked them whether I can view the hearts first from the bottom of the diamond), but I am not sure "view" is actually physically viewing or just virtually viewing. I think non-mainstream/non-commercialize stores won't keep too much stock in their inventory, but you can try to make appointment and ask to view the actual diamond, see if they can accommodate you or not. This is for you to check on the appearance of the diamond to see if you like it. You can also take this opportunity to check on the workmanship of the ring setting, which I think it is important as well, especially the prongs - you need to make sure it can hold the diamond well. Besides that, you can also examine the weight of the ring setting and see if you like it, you may also ask if they can provide you the details like how many grams of gold they use and what is the total weight of the ring setting. Also, try to get the ring size as accurate as you can because if there are more than 2 sizes increase in ring size, there may be a surcharge for the extra gold needed. Do share with us the GIA cert number if you need further analysis.

Good luck! 

Why don't you just make an appointment with Eumayco and check things out first since they have inventories.

Yup,  correct.

What you gave is very limited info.  Like I said, get the GIA number for all of the diamonds. Otherwise, nothing can be determined through here. Next time, ask for GIA cert and takr picture.

I assume the price above includes ring? Otherwise it is really expensive.

If you want to marry in church, then you have to find the church that is able to provide you such service. For me, I did it in Thean Hou Temple. Before going there, I need to get some forms from the govt. office at Jalan Duta. I filled up the forms there and then as well. Can't remember which forms already, but I believe you can ask your church and see or just go to jabatan perkahwinan and tell them, then they will assist you accordingly. You will need to prepare passport size photos for both husband and wife. I think actually can mix different background colour, but just to be safe, just prepare the passport photo with same background colour. If both white, then both white, if both blue, then both blue. After filling up the forms, you will have to find commissioner of oath (pesuruhjaya sumpah) to stamp your forms. You are able to find one of them at the same govt building at Jalan Duta, so it is convenient there. A fee is required (I think around 10 ringgit, not sure, but it is not too much). I finished all the forms stuff less than an hour during weekdays. After that, I can proceed to hand the form to Thean Hou Temple, choose a date and time, and pay the necessary fee.

The benefit of using a temple/church is that both couples do not need to change the state on the IC.

Anything else, you can just search in forum or google. Better still, just call up jabatan perkahwinan or chuch to ask.

Good luck!