For the most part, cpu and ram are not with a decent computer if its just sending random data or 0s. You can either have them buy dedicated disk wiping bays, which are automatic and require no computer, or if you want to be cheap just get those drive docks, the usb ones that look like toasters and are about 30-35 US.
Dedicated drive erasers that do a configurable number of multiple passes and random data are more expensive that usb docks, but you can go for the 2-3 bay versions which are typically the price per bay and just stack them up. These were my preferred solution, the right ones you slap it in and you don't even need to press a button if it's configured like that.
If you go the cheap route and use usb docks, you should use USB 3 if you have it (this is your problem likely), and you can use hubs, just keep bandwidth in mind. Each mechanical drive is probably capable of somewhere in the neighborhood of 90-150 MB/s sustained writes (720-1200 Megbits/second). You don't need 100% as doing more at once is the goal, just keep it in mind. One proper port with the full bandwidth can do 5-6 mechanical drives without much slowdown, where USB2 will only get you 60MB/s on one drive. You can add a usb3 pcie card if needed.
https://www.amazon.com/Inateck-Express-15-Pin-Connector-KT5001/dp/B00FPIMICA
Check their supply storage, most places have at least some usb drive docks, see if they have any good usb3 ones to get you started. If you need to buy them, check benchmarks with both bays going on cdmark, you'll see that in amazon reviews a lot. Even if it's slower, if you can get a fuck ton going at once, that's better too.
Try to match the sizes kind of if you can so they finish around the same time and you don't have to babysit. Put a group in before you leave too if you can time it.
As for the software, I don't know what they are using, but make sure it works with usb. Some bootable ones have trouble if not configured right, but anything in windows should work ok. Make sure you are at least writing all 0s to the drive, and if they require random data writing, then do it. Do only the number of passes the policy requires- and if they don't require multiple passes don't do it, save time with that many drives.
At 2000 drives, this is sounds like a large volume and may be a recurring problem. The alternative is to ask to build a specialized solution. Get the cheapest build with a case the can be filled entirely with 3 bay 5 drive hot swap bays. Or buy a premade solution, but they will cost multiple times more. If you need to work with like SAS drives from servers at a later point, keep that in consideration. Keeping an old decommissioned server with front hot swap bays is cheapest there.
Finally, I know in this case they want to reuse, but if they're saving a buck and want you to completely destroy without the automatic equipment in the future, ask for a cheap drillpress, or a cheap corded drill and good bits. Press is easier, safer, and better on your hands though. This is the fastest destruction method that's cheap. You can get a couple hundred drives an hour easy that way. With drives that are marked for destruction, check that they don't have any special policies, like matching DoD or NSA standard or something, like degaussing, which requires specialized equipment and is stupid because it does nothing a few holes or shattering cant unless you got like the fbi or something looking into you and even they would have a hard time- at which point metal shredders are cheaper and funner, though a liability possibly. Some larger companies like to match their policy with shit like this, looks good to upper management or something idk.