Hard drive replacements are a great way to improve storage space or even overall performance to your device.
Solid State Drives - This device comprised of memory chips that store all your data allows for incredibly speeds even for older machines. This replacement is higher in price for less space due to the speed increase that you receive.
You can expect to pay $85 and up for a reputable solid state drive (based on the Samsung EVO 860 500GB SSD)
Hard Disk Drives - This device is comprised of a "disk." Think of it as a "record player". There is an arm that reads data and a "record" that stores the data. The price point of these devices are cheaper with the benefit of more storage but costs you in a severe decrease in overall speed.
You can expect to pay $35 and up for a hard disk drive for a 1TB (1,000GB) hard disk drive.