Cheap things to do in Miami or nearby?

Hi my fiancé and I will be staying in Miami in May. We're eloping on a beach nearby. Also doubling this as our honeymoon. Are there and things we have to do while we're there? Fun day date places. We're not really into partying. Also recommend some of the best cheap eats? We plan on only doing a few nice restaurants and the rest cheap eats? So what are your fave upscale restaurants and fave cheap eats? This can be in Miami or nearby.