I don't think ~100 Euro is out of range for this hotel, especially for May when they're likely to start getting more tourist traffic going through. I've stayed there for less in the past, but it's not a bad rate for what is a rather nice hotel.

To your point though, I did notice a jump in Starwood rates in Poland recently. I'm booking elsewhere there and rates are a bit higher than I've been able to get in the past.