In fact having it ready to go might help you clinch the deal. If you're part of an evaluation and you're ready to proceed and your competitor has to go and get this setup - you're more likely to get that business. Likewise if you're the competitor who's been caught with their pants down then you're more likely to lose that business. Every salesman I know is always looking for something to give them an edge for closing a deal!
My former company sold on-premises enterprise software. Sales were usually a monthly fee in the $10k+ range.
Our company started quite small: 4 people, and in Australia but selling into the US and UK mostly.
Basically every one of our customers wanted source code escrow. The cost to use was minimal, both in effort and for the escrow agent.
It's not zero effort, but it's not that hard. There's plenty of firms provide the service.
Every time my former company shipped a release, we'd bundle up the source code, libraries, build scripts, etc, burn a DVD and send it off to Iron Mountain. Every time you do a sale that wants escrow, you add their details to the list and send that off to Iron Mountain too.
These days, I'd probably ship a Docker or VM image from the CI system: you need to give the customers something they can use to create their own builds.
We had some customers who actually tested the process, and when the company was sold and the product canceled, one customer took the option of getting the source code, and continued to make their own builds for a bunch of years afterwards.
ie. It shouldn't be at the suggestion or cost of a single customer, it is an accepted business cost to you.