Well you don’t have to buy them brand new. If you guys have a used goods market there, you could look around for some good deals on used drives there. Or even used PCs, sometime people sell entire PCs for the same cost as a hard drive, so look out for those and take the drives out, sell the rest of parts.
And if things are really desperate money wise, it doesn’t even have to be a hard drive, you could even store your music on CDs/DVDs - not the most convenient option I know, but it’s an option - you could move the music that you don’t listen to often (or music that you’re tired of playing constantly), and keep your more frequently played music on the HDDs.