Thanks for the suggestions guys. I am trying a second hand P Johnson cotton jacket on tomorrow. If it fits I will take it. If not, I will walk over to Herringbone and try their two cotton jackets. If none of those are a go, I will try Sports Craft et al. I like the Boglioli jackets Pink Socks, but they are outside of my price range at this stage.
I think that $350 for an odd jacket is excellent value, if it fits well. Herringbone's jackets are quite well made and I've got four or five of them.
Depending on your personal preferences (and I don't want to turn you into someone who is obsessive about such details), you might want to check the lapel buttonhole on the Herringbone odd jackets because, in the past, some of the cotton jackets had "keyhole" lapel buttonholes, rather than straight cut buttonholes. Some people don't mind that at all, but I have a strong preference for straight cut lapel buttonholes.
Another option is to go into your local Polo Ralph Lauren store and try on some of their Polo made-in-Italy suits or jackets (which are made by Corneliani) and then see what you can find on eBay, as you can typically get new-with-tags (NWT) Polo clothing on eBay for 25-50% of what it retails for here.