Regarding HDDs, here's a brief overview.
I recommend buying HDDs only from these manufacturers:
Seagate, Maxtor. Avoid the others.

Here's a list without prices. Otherwise, they'll say I'm running a store or providing a price list.

Okay... The prices for these hard drives are currently dropping. If you need an additional drive, choose one from this list (prices range from 1050 to 9000 rubles). 9000 rubles is already for terabyte drives.

Seagate
1) 120.0 Gb HDD Seagate (ST3120811AS) 7200 8Mb SATA-2.
2) 80.0 Gb HDD Seagate (ST380815AS) Barracuda 7200.10 8Mb SATA-2
3) 200.0 Gb HDD Seagate (ST3200822AS) 7200 8Mb SATA 2
4) 250.0 Gb HDD Seagate (ST3250310AS) Barracuda 7200.10 8Mb SATA-2.
5) 300.0 Gb HDD Seagate (ST3300831AS) 7200 8Mb SATA 2 = 2707 rubles.
6) 500.0 Gb HDD Seagate (ST3500630AS) Barracuda 7200.10 16Mb SATA-2
7) 750.0 Gb HDD Seagate (ST3750640AS) Barracuda 7200.10 16Mb SATA-2
8) 750.0 Gb HDD Seagate (ST3750640NS) Barracuda ES 7200rpm 16Mb SATA-2.
8) 1000.0 Gb HDD Seagate (ST31000340NS) Barracuda ES 7200rpm 32Mb SATA-2
9) 1000.0 Gb HDD Seagate (ST31000340AS) Barracuda 7200.11 32Mb SATA-2.
10) 500.0 Gb HDD Seagate (ST3500320NS) Barracuda 11 ES 7200rpm 32Mb SATA-2
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Maxtor

1) 80.0 Gb HDD Maxtor (STM380215AS) DiamondMax 7200rpm 2Mb SATA-2
2) 80.0 Gb HDD Maxtor (STM380815AS) DiamondMax 7200rpm 8Mb SATA-2
3) 200.0 Gb HDD Maxtor (6B200M0/6L200M0) 7200 8Mb SATA -2=
4) 250.0 Gb HDD Maxtor (STM3250310AS) DiamondMax 7200rpm 8Mb SATA-2.
5) 300.0 Gb HDD Maxtor (6V300F0) 7200 16Mb SATA-2
6) 500.0 Gb HDD Maxtor (7H500F0) 7200 16Mb SATA -2
7) 320.0 Gb HDD Maxtor (STM3320820AS) DiamondMax 7200rpm 8Mb SATA2

Generally, they cost around 2000 rubles, give or take