A new hard drive of similar size will cost tens of dollars. An SSD that's a fraction of the size of your current drive will be tens of dollars but it may not be big enough for what you need. You've had errors using disk utility, you've had errors gparting the drive, and it sounds like you had errors with DBAN. In other words, you've had errors or problems with every utility you've used on the drive. If it was something more subtle or difficult to trace, then I'd recommend Scannerz as well, but in this case almost everything seems to be saying the drive already has problems.
If the drive is an OEM drive put in by Apple it's likely slow. Some of the newer HDDs (if you go that route) have throughputs with disk to system transfer rates approaching SATA I interface speeds, which, for an HDD, will seem like night and day compared to the original drive, and an SSD will be even faster (just costlier). The dead give away for a newer high speed HDD will be AF formatting and the specs should reveal a high disk to system transfer rate (don't confuse that with controller to system speed which will be nothing more than the SATA speed of the system/HDD controller buffer transfer rate).
If the system uses a 2.5" HDD, my favorite of the new breed of AF formatted drives is the Hitachi 7K500 drives (7200 RPM, 32MB buffer, and a media to system transfer rate approaching 1.4Gbits/sec. and 500GB in size) Here's a link:
http://www.hgst.com/sites/default/files/resources/TSZ7K500_ds_v3.pdf
I got one of them for about $45 a year or two ago.
