You refer to yourself as an agent in Miami Beach, but you say your are a Swedish citizen, so I'm bit confused. I've answered this question about the difference between co-ops and condos many times for consumers here, so please refer to my previous answers. Without repeating it all again here, and with others offering their explanations below, a coop is not suitable for your purposes as you cannot rent it out at will. Co-ops have very strict sublet regualtions. Furthermore if you are not a US citizen, a condo would be your only option.
There is no "Essex Park" neighborhood. Are you referring to the Lower East Side where there is an Essex St. and an Essex St. subway? Are you referring to the south rim of Central Park where the Essex House hotel is? As far as average price per square foot in any particular neighborhood of Manhattan, factors like the floor it is on, the view, the condition, whether there is a doorman, concierge, elevator or walk-up, etc. make giving an average very difficult. More specifics are needed.