Thats the one.

You will find many unlocked units. In the United States they can be bought for below 30$.

Be aware however, that the keyboard and general handling of the Droid4 come nowhere near the N900 (for me) and that the lack of usual modifier keys is annoying. Although I am sure Leste has a sensible keymap.

The Sailfish port for the device is in an not-yet-usable state and the last Lineage OS came early 2019. Multiboot is easy.

Edit: @deutch1976 I wouldn't call covering the shipping costs "bought"