It is certainly time to move on
but, as Bob pointed out, hard drives are relatively inexpensive.
I can only guess but my guess is that you have a cathode ray tube type iMac, kinda teardrop shape, which takes a regular ATA type hard drive and will accept at least a 250GB drive.
Replacement is reasonably straight forward and there are "Take Apart" guides all over the internet.
Basically a intermediate job for someone with a working knowledge of a screwdriver.