Not 100% sure on price really. Think your right about the size being similar to the mega horn. Mine has a stovejack fitted in.
i don't have a nest for it though.
It has indeed, just Velcro on and off. I have the bathtub groundsheet but received a bit of damage from the fire so cut a square out. Could be repaired easy enough, I ended up using a fire blanket to protect the floor.
Make me an offer via PM.