I agree 100%!  In order to provide a quote, I'd have to work to determine the amount of time.  This is work for free.  I don't work for free, and neither should anyone who values their work.

It is made clear - repeatedly - that we will not provide a quote, but an estimate.   If the potential client cannot accept that, it spells trouble I'd rather avoid anyway.

$500 should be the base for a commercial abstract - especially for a 100 year commercial abstract.