in Europe there are several smaller ships that fit your figures. But most are quite old by American Standards. All are based on Piraeus:
Monarch Classic Cruises (http://www.mccruises.gr
) offer the epitomy of a Greek Islands cruise: The "Golden Fleece" Itinerary (7day), for which Royal Olymic Cruises, and before that Epirotiki Cruises was known for, which includes also Istanbul. Also they offer 3- and 4-day Greek Islands cruises. They took over many employees from these older firms.
Golden Star Cruises (www.goldenstarcruises.com
) offer 3-night and four night cruises on the former Adriatica liner AUSONIA now named AEGEAN II. This ship is more for the classic liner lover.
These itineraries can also be had from Louis Cruises, the biggest competitor in this field. (http://www.louiscruises.com/cruises_...eece_home.html
It might be tricky to book them in the US. Probably they even have a North American Sales representative or GSA. Hope that helps.