Decided to try LocoPCB who support V-cut panelling of a single design for no extra charge. This to experience V-cut panelling and to write a review of my experience with them. LocoPCB also charges $2 for 5 boards, for the first 5 orders. Here is  ongoing story until the boards are received.

Previously I checked PCBWay who is having an end of year sale so I decided to see if they'll do panelised PCBs, 2 per board, for the offer price. Unfortunately they want to charge extra for the slot, breaktabs, and mouse bites I put in. But I'll see if I can send another project in to take advantage of the offer.

Then I checked JLCPCB who didn't object to a panelised board last order, and the normal price is good anyway. It turns out from reading their help page that JLCPCB have no extra charge for breaktabs and mouse bites provided it's a single design.