I cannot give brand or cost advice because the last A/C that I replaced was through a friend who owned an A/C company and I got a huge discount.
I can give advice on going too big. The house called for 4 ton, I wanted a 4.5 because 100+ temps in N TX. A 5 ton was installed because they did not have a 4.5 in stock, no extra charge. It was great in the summer. The unit still cycled even on the hottest days. However, spring and fall sucked. The A/C did not run long enough to pull the humidity out of the house before the set temperature was reached. If you oversize, don't go too oversized. I suppose a multi-stage compressor could have solved my problem.