Let's lock (up/in) that deal.
I can't find any lexical support for any of these usages. I especially looked at the Free Dictionary's phrases, but nothing under lock up or lock in is relevant.
There's a website called "Lock The Deal", but I wonder if "Let's lock the deal soon" would be something commonly said.
I also came across this: https://forum.wordreference.com/threads/lock-up-deals.1319685/
This is a sentence from Time magazine:
These governments are desperate to get capital into agriculture," says von Braun, who believes the drive by giant companies to lock up land deals could benefit poor African countries whose governments negotiate wisely.