It depends on how bulky the figure is. If it can be flat-packed, so that the figure plus padding plus the envelope is less than ca. 20mm thick and less than 500 grams in weight, I think it should be postable by using the Grossbrief International for 3,45 Euros (the "letter" thing is usually measured by the post office worker trying to push it through a letterbox slot template).
I have used the Maxibrief rating for small parcels before, so it should work. Note though that these options aren't insured per se, which I suggest for the 28 Euros option (insured small parcel), and it pains me to say that, with DHL being what it is these days, one should shell out for the recorded option if the item has any monetary or intangible value.
So, a single 28mm figure, unless there is a 25mm or larger base attached which cannot be removed, should be able to be posted by Grossbrief.