Hi Paul,
It's A5 , we used to buy them but even when we were buying 5,000 at a time they were still around the 35-38p mark.
We now make our own, we have a Risograph machine and buy in A3 paper, we also have a commercial guillotine and clamp. Our techs if they have a quiet afternoon or gap in the day print them, then make first cut, glue them, then cut those down to the A5 size. We no longer apply a backing board, so we're just making HUGE thick glued stacks and split those down as needed. We leave every client one with the job, about an inch / inch and half thick. The 5 arounds are about 10mm thick with the stickers on, and we also leave them on desks while cleaning commercial premises. We usually manage to keep on top of having them available just fitting in the making around quiet afternoons or short notice cancellations we don't manage to fill. Obviously this time of year is a bit quieter too so we've got a stock on now. I've not worked out a unit cost recently, and paper prices have gone up, but it just gives us flexibility to leave thicker pads with the client, and blocks a couple of inches thick for commerical buyers too.
The notepads turn up everywhere, i've stood behind people at Checkouts and they have their shopping list on a sheet.
It depends what you charge, obviously, but even at 40p each I think they are worth doing, particularly if you make a point of knocking on the door and introducing yourself and saying you'd just like to leave them a leaflet and notepad in case they're interested in future, then shut up and leave, no pressure. That's what I did when i was on the tools and it worked really well. Now, our techs don't like the actual knocking on the door bit, so we just put the notepad through with a leaflet, doesn't work as well but still works well enough to justify it.