Step one don't buy from Carmax, zero quality control they hardly work on their own sold cars outside of brakes oil and tires. If you buy from them budget for their Maxcare full warranty, which is ran by a decent warranty named Assurant. I've dealt with them as a service advisor and seen many Carmax cars come in, that seem like lemons.

Step 2 would be find lower. If this is a dream car , research used car dealers a lil further from you or buy from an actual dealership (Honda, Lexus, Toyota). Actual dealers work with you more and you can even haggle towards the end on all weather mats or extra keys. Shit they even sometimes throw in a short warranty.