I develop b2b apps for several companies - does apple require $299 per customer for me or I have to pay for it once?
Publishing B2B proprietary Apps
If you are publsihing apps for your customers via the B2B Program all you need is a standard developer program account. All your customers will need is a Volume Purchase Plan (VPP) account.
Take a look at the B2B Program page for more information.
What to do in countries where VPP is not allowed, for instance Colombia?