(I hope this is allowed!)
My idea is to post them from Germany when I'm visiting there at the end of August, as it's usually cheaper there than here in Spain, and send a paypal request once I know the exact price. (Or I could first ask at the post office, if preferred.)
Graded readers for Dutch, aimed at native speakers of German:
Then I have these language coursebooks and workbooks for German.
They have been used in a language academy and are thus worn, but nothing's written inside.
They are old and not up to date and would probably be interesting to either a collector or maybe someone interested in the exercises.
Then there's this book with basic German vocabulary for native speakers of Spanish, with translations into Spanish and example sentences:
Graded readers for Italian, aimed at native speakers of German:
