Can you even buy 500 GB HDDs these days? I can get 1tb drives from my local Officeworks for $63AUD, but that's pretty uneconomical when you can get 10tb drives for $360AUD.
Get the largest SSD you can, and buy a HDD later on when you can afford it. You can get slight discounts on HDDs by buying external hard drives and "Shucking" them (removing the casing and using the disk inside). You may need to do some research to work out if it's possible for the drive you want to buy though, not all are shuckable
Never understood why that is but does seem to be the case often enough. So selling the drive with extra parts is somehow cheaper than the bare drive...
I think it's an economies of scale thing, more people buy external drives than bare drives, so the price drives down? Does feel very wasteful though, I have a heap of e-waste drive cases :/
Sometimes it's because they use cheap Shingled Magnetic Recording (SMR) drives in the external enclosures. These drives are slower and less reliable than the Conventional Magnetic Recording (CMR) drives. Some of the cheaper internal drives are also SMR these days. An SMR drive is OK if you just want to write data to it and leave it there, and you're not too worried about the transfer speeds. But if you're doing a lot of intensive activity with many writes and rewrites, it'll slow you down.
They are often Green drives as well. But the latest 10TB ones I bought and shucked a few days ago from WD are not SMR as far as I know? If you are careful with the disassembly and buy from a place with a good returns policy you can always return it if it's SMR.