Switching to Pro Plan for 1M Clay Credits Inquiry

Hi there Clay support team, I'm on a starter plan but just landed 1 client that needs almost 1M clay credits to enrich and clean a huge database. I'm considering moving to a Pro plan and buy extra credits to finish this project fast and after, I'll move back to the starter plan. Is this possible? What's the best and cheaper way to get this 1M credits I need?