That may sound high for a lot less than an acre if the owner doesn't understand what the difference between raping the lot and leaving it look nice.
If I was dealing with 3/4 AC of mature oaks that needed to be disposed of, $2500-3000 would not be out of the question and I've charged as much as $4k an acre when the trees were big, bushy, and everything had to be chipped in tight quarters.
I just bid a lot about the size you are bidding. Called for everything cleared including all stumps dug out and mulched and it was dense with 8-10" dbh cedar and a few oaks and hackberry trees. I bid $3500 and was beat by a guy who said he would haul it all away for much cheaper. I estimated somewhere around 65-70 yards of shreds/mulch AFTER everything was ground up. I can only imagine how many trailer loads of brush and stumps that guy will haul out of there and there aren't many legitimate places to haul brush.
Hopefully you made a good impression with the owners and they won't opt for some cheaper yahoo that butchers those lots. Your plan will leave it looking good but it costs more to do that and hopefully the owners understand.
"You Can All Go to Hell, I'm Going to Texas." --Davy Crockett