How to accurately calculate ppd for international printer parts shipping?

[Styloid]

We are building a site to sell printer parts.

They will go internationally.

If they don't ship ppd from us they can take a lot longer to arrive.

Our volumes will be low and we cant upgrade to shopify plus, the cost is to high and we might as well go back to ebay. which seems to offer some help here.

Should we just guess  a percentage and add it on?

Peter