I want to show shipping costs on product page.

[dbltoe]

The real problem is when someone orders more than just the one item. How would the other item effect the total cost? Will two "priced-individually" items ordered result in a shipping cost that the customer will balk at?

I think you're creating more havoc than help.

Figuring by weight and price is already in ZC BUT, it is based on order_total.

[ellipsis]

Well I've solved this now.
into tpl_product_info_display.php find the line that does the price.
Then added:
if ($products_weight != 0)
echo ' <span style="font-size:70%;">Delivery &pound;' . $products_weight . '</span>';
Works OK for what I need.
It's really rather a hack though. I don't use the built in zen cart shopping cart system and instead just link to amazon. But I think this would still work correctly if I did, shipping pricing is worked out by the combined product weight so it would still be correct.
If it's not obvious you just set product's weight to the price of its shipping.