- Yes, the firms can be trusted - caveat pay attention to ToS. Take note of which ones will certify destruction of the drive, some even cover PCI liability.
- You can run DBAN (or similar tools!) yourself, from any system w the right connects, on as many drives as the chipset can manage. Then you can resell or donate drives. Yes it takes some time, but unless it's a drive that predates UDMA, it's not going to take too long unless there are r/w errors - in which case just punt it to the next method.
- Power drill + hard drive = pretty sparks. Alternatively, you can just disassemble the drive - I find the metal platters make very nice coasters.
ps: Degaussing is not considered sufficient for business use, so if you're concerned about data destruction it's not the route to go.