If all you need is PCBs, I highly recommend OSH Park, at least if you're in the US. They have fast service, their PCBs are very high quality, and I've always found them easy to work with. Nearly as cheap as the cheapest houses in China, too!

If you need a PCB with components ("stuffed") then in the US I've had good luck with Macrofab, and in China I've used Seeed build-to-order; I've found Macrofab easier to work with than Seeed but Seeed weren't bad, just not as good.

I recommend to use Pcbway. register through the link below to get 5$ coupon which you can use to get your first order fabricated free of cost  5-10pcs with 24hours free service. they ship their pcbs to almost every corner of the  globe

https://www.pcbway.com/setinvite.aspx?inviteid=326146 

they are very much professional in this field and that is the reason i call them engineer friendly.

I submit to JLCPCB about once a month. Right now i have a little less than 100 pieces in production and scheduled to finish in the next day or so.  They have always offered excellent customer support on the rare occasion that something is wrong with my files.  I also really like the fact that it is extremely easy to add to an existing order.  For example, this round i had two sets of higher qty boards that were submitted to the production line and also had gold fingers and V cut so that takes a couple of days longer.  while waiting for them, i submitted a couple of other simple 2 layer boards that go through the much quicker prototype line.  They will all be done about the same time.

For bigger boards and high quantity you are better of forgetting the small manufacturers that deal with the predefined sizes. Try a bigger one. I have used allpcb which has very good quality and speed. 

I wouldn't call the fabs often mentioned here as small. Many of them do handle large and complex boards. 100x100 is a historical artifact. Of course you can ask for larger boards if you pay. Probably hobbyist jobs are used to fill panels containing larger designs for higher value customers. That's also probably why orders are quantised to multiples of 5.

I did not mean the ones mentioned here are small. Just that a lot of the companies that do this hobby PCB thing with 5x5, 10x10 etc are actually small in the grand scheme of things. 

JLCPCB often mentioned on HaD caters to hobbyists but I wouldn't call them small as the conglomerate includes EasyEDA and LCSC. There's nothing to stop you entering a larger size if that's what you want (up to the size of the panel), you just pay accordingly that's all. And anyway if it's adequate why pay more than necessary?

I am located in Perth, Australia. I need to manufacture a total of 50 boards. They will be about 10cm X 15 cm in dimension.

There's a significant price jump at 10x10 cm. Maybe you could split up functionality to stay under this limit even if it means more boards. Also minimum quantity for each design is 5 so if you can factor out common functionality that would help. Anyway play around with the figures on pcbshopper.

Shipping often costs more than the boards. In the current coronavirus situatiion, the slow methods are likely to be slower.

There is a lot of choice. I've tried a few of them and they were all fine for my undemanding projects. I've reviewed a few of them on my pages. Looking at your project I'd say any of them will do. There is a price comparison site at https://pcbshopper.com

Industry standard for fabrication info is Gerber.

Thank you so much!!

Where are you located? Approximately how many PCBs and how large?