This is for a creative writing project, and I'm looking for a little accuracy. It's fiction, so it doesn't have to be perfect, but I like to be reasonably accurate in the things I write.
So, here's the question: Assuming the person is wealthy enough and high-status enough to be able to afford nice things and also travel as necessary, and that the person was too high status to know how to glean it from the natural environment, how difficult would it be?
Edit: By German, I mean someone who lives within the Holy Roman Empire, not too terribly far from the Black Forest, at or around the year 1230.
So not exactly your location or time period but everything I know about Sulphur in the Middle Ages I know in the context of gunpowder weaponry and the earliest examples I know of that are from England. Still, if you're only using this for Fiction it might be close enough for you.
T.F. Tout in an article that's a century old but still great went through various rolls (government documents essentially) and pulled out references to guns and gunpowder from the 14th century. The components for gunpowder were often bought separately so he could get an idea of pricing for Sulphur (although it wasn't his main focus so he didn't publish every reference). In 1347 Sulphur cost 8d. (that's pence) a pound and in 1379 it was 6d. a pound. I wouldn't assume the cost necessarily dropped between these two since these are two different transactions that could have another reason why the cost was different (different merchants selling for one thing). As a point of comparison 6d. a day was a high wage for a skilled worker (the kind that made gunpowder and guns in Tout's example).
In the Fourteenth century most sulphur apparently came from Iceland which produced a lot of the stuff thanks to it's abundance of volcanoes.
The article is T.F. Tout 'Firearms in England in the Fourteenth Century', The English Historical Review, Vol. 26 (1911). 666-702.