You mention they are a customer,
so you either have a conflict of interest,
or you hope to build a stronger relationship.

Quick research will tell you that gaining new customers is far more expensive,
then spending a little to retain a customer.

So, if they are your customer, and not your friend,
would you consider having enough of your machines moved to a private banquet facility,
or hotel banquet room, to host the party, with your machines as the entertainment?
.Local estimates is $350 to move each machine, with a declining cost for multiples
.The risk of the insurance are mostly carried by the professional hall
.The customer can rent the hall direct, and get what they like (food, beverage, cleanup fees)

Are you in the game rental or banquet business? If not, is that what you want to be?

20 is beyond pushing for a favor, while a 6 person dinner party, and you would not even had posted here.

re:How Much Would You Rent Your House Out For?
$7,000 would buy me a new machine of my choice, so let's start there.