"How do I respond to these price objectors who demand a whopping 86% in discount,"
Say no…
" yet interestingly enough they are the MOST demanding when it comes to support and feature requests."
… because of this ;-) If you have happy customers at the higher price point I'd be investing my time trying to find more folk like those — unless you think that a lower price point is going to give you a much, much larger market.
" would I tell them that they might not be a good fit in a polite way?"
I dunno what & how you're selling — so hard to say. Me — I'd lean towards just saying "Sorry, no. We have a standard pricing structure for all clients." If you're offering just monthly pricing maybe offer them an annual plan with 12months for 11months of money. That would at least help cashflow.