I want to give my wholesale customers their own sign-in that will automatically change the prices they see through varying discount levels.
My number one recommendation is Customer Pricing by Bold Apps. It lets you set really specific pricing levels and then assign those levels to customers with tags, so they'll only see the prices they get, not anything else.
Check it out here: https://apps.shopify.com/customer-pricing
Let me know if that doesn't work for you. :)