If you dont need the drive to be fast and want best bang for your buck storage capacity, HDD is the way to go.
If you want speed and are ok with a higher price, SSD is best. Used enterprise HDD are usually a good value. Im in the US so not sure about where to purchase exactly.
Something to consider is if the drive you are storing the os and files on are the same, using am HDD will make it slower on start up.