Mark-
I can't guarantee all WiFi AirPrint printers can be set up with an Ad Hoc network, but I know some can. To be sure, you would need to contact HP about a specific model.
Mine is probably the cheapest AirPrint model, the HP D110. (Outside the US, the equivalent model is B110.) It was set for an Ad Hoc network when I first plugged it in. In the initial setup, I associated it with my regular network, and downloaded a firmware update in the process. You will most likely need an update regardless of which model you get, so will need access to the internet for initial setup.
As I recall, I was able to set up the D110 for Ad Hoc networking by specifying a non-existent network name. When the printer couldn't find it, it asked if I wanted to establish an Ad Hoc network. There was a nonsense error message along the way. I ignored it and the setup was successful. There is probably a more direct way to do it if you search the menus.
Fred