Research on my part indicates that the Mellotron on ebay from Patsy's dad's studio has the following provenance...
none.
Patsy's dad appears to have been a nobody and this Mellotron was not used for anything well known.
I also have read that Patsy neither sang on nor played any instruments on, "Grandma Got Run Over by a Reindeer."
She and Elmo are divorced.
Elmo paid $50.00 for the song. Elmo's a vet.
Patsy seems to have disappeared.
Who ever pays what they are asking for that Mellotron will probably be (a) Patsy.