What is the best way to keep your audience engaged? eye contact smiling explaining how your proposal will cost them less than it will benefit them explaining how your proposal will benefit them less than it will cost them explaining how your proposal meets some of your needs or goals

The best way to keep your audience engaged is to give them a reason to listen. People are selfish, they think "Well, how does this benefit ME?" They might pay a little better attention if you make eye contact and smile, but if you aren't attractive, you might lose your audience completely, haha! But, seriously, people will listen if you can tell them how to get something they want (even if they didn't know they wanted it). 

explaining how your proposal will cost them less than it will benefit them

Eye contact, explaining how your proposal will cost them less than it will benefit them
this might be right. i'm sorry if it isn't.