<p>Not everyone is cutting back as the economy tumbles. Or, at least, that's the hope at Residential Cruise Line -- the latest entrant into the rarefied world of super-luxe floating condominiums.&nbsp; </p><p>The Phoenix-based company finally opened sales this week for what's billed as the most luxurious residential cruise ship ever -- a 76,000-ton vessel that will have 210 units priced from $2.8 million to $18 million. </p><p>The line also will hold an inaugural, invitation-only sales event on Dec. 15 at Dubai's Burj Al Arab hotel.</p><p>In the works since 2005 and scheduled to debut in 2011, Magellan will offer an elaborate mix of amenities including a tennis court, putting green, four fine dining restaurant, an observatory, all-weather heliport, spa, Broadway-style theatre and two pools. Among its most unusual features: A retractable marina on the back of the ship that will have room for lounge chairs. </p><p>Residential says the ship will cost $1.2 billion to build. </p><p>As on other residential ships, passengers will own their cabins outright and can hop on-and-off as they like. Residential also is selling time-shares on the vessels. </p><p>The least expensive residences on the ship are two 624-square-foot cabins that come with a single bedroom and bathroom and cost $2.82 million. But prices quickly jump to more than $4 million for the smallest two-bedroom condominiums (1,130 square feet). </p><p>The ship's most luxurious digs, two $18 million Portofino penthouses, come with four bedrooms, five bathrooms and measure in at more than 4,300 square feet.</p>