Alsace- May weather - AC needed?

You can find actual, historical, day-by-day temperatures for most cities and towns on the website timeanddate.com. I find that much more useful than monthly averages. The latter hide extremes and are often based on time periods that cut off many years ago. The climate charts in most cities' Wikipedia entries, for example, are based on weather up through 2010.

Here's the timeanddate info for May 2021 in Colmar. Definitely go back several years (I usually go back 5 years), to get a good feel for what you might run into.

And here's Strasbourg's data for May 2021.

Humidity is typically much lower, than, say, on the US East coast in summer. And the likelihood of a heatwave with high nighttime temperatures is low anywhere in France in May.
However, a room with AC won't necessarily be more expensive. It is merely likely to be less charming, since older/traditional hotels are the ones without AC.

We were in Colmar in mid-June 2017 and they were having a heat wave. I'm from the southeast US and I know heat! The humidity was not as bad as what we're used to here. We were in a place with no A/C and the first night was pretty uncomfortable. The second day we went and bought a 20 euro fan and the next two nights were fine.

Thanks everyone for your input. I'll take a look at these historical weather patterns and go from there. Merci!