I thought it was Essentially, heh. Since that word means nothing, max low $$ because.. well even though selling it is probably unlikely if you do get lucky, itll probably be for that amount.
Yes, it is a valid dictionary word. http://www.thefreedictionary.com/Essentiality http://www.answers.com/topic/essentiality http://www.merriam-webster.com/dictionary/Essentiality http://www.yourdictionary.com/essentiality http://thesaurus.reference.com/browse/essentiality ... just to name a few. Google returns about 955,000 results for "essentiality" term.
You know, this is a tough one to appraise. I can't put a dollar figure on it. However I like the sound of it. I think it's highly brandable.