A quick google says that we can get caps printed under $15; depending on who you use there are minimum order quantities (eg 50 or 100). Some places that are more expensive will allow you to order lower quantities.

I think you would go with the AUSSIEPINBALL.COM wording as per the banners - I imagine this would look quite effective as yellow on a darker colour.

If Gavin is in agreement then picking them up from his stall is a great idea - saves on the hassle of organising delivery beforehand. It would be sensible to implement some sort of basic ID check (like driver's licence).