Not cheap. On Amazon one can find much cheaper ones but who knows…
I had similar considerations about using my Novation Launch Control XL in order to control some of Midihub’s parameters. However I won’t buy an additional USB MIDI host but will use an already available MIDI controller with DIN MIDI output.
You need a USB host in between other USB MIDI devices and Midihub to forward the USB MIDI data as needed. You can make use of your computer/laptop for this purpose, or probably the smallest possible footprint for this purpose would be mini computer like Raspberry Pi and clones.
There is smaller and better one - original CME WIDI bluetooth connectors (expansive), or - for this case may be even better - chinese, wireless connectors (two in one pack): DIN5->BT + USB->BT. It connect together very well. It may be connected as standalone BT devices or as pair (DIN5<->USB).
USB version may be connected from one side to powerbank, and from second to usb midi device. And viola, your USB device is wireless now