Depends on the geography and/or whether the knowledge is highly specific.

As a datapoint, the average Dutch contracting rates I see for IT development (think: Java, Swift, Kotlin) range somewhere from €75 - €150/h. Higher is possible, but then you're talking very specific expertise and typically shorter projects.

I'm on the hiring side, this is a figure across some 20 external devs. I think it's representative of the middle of the market.