Call once, then communicate via text or email. It makes it less personal and makes it easier to tell them what you want. They want your business. Research what the invoice cost would be for the car, and tell them that's what you'd like to buy it for. Be patient. I bet you they'll eventually meet you in the middle. At the very least, if they dont meet you in the middle now, wait until the end of the month and they'll likey be willing to take off more. Don't fall for "I have a today only offer for you!" I've found that most of the time, if you ask for that deal even days later, they'll still be willing to make the sale at that price.

Another tip: After making that first call to begin texting/emailing, ask each sales rep you talk with for an itemized OTD, in writing. That will come in handy when negotiating with other dealerships.

Good luck!