In general, I would think that SXM would be a hard get for just about anything over a full size car, especially for the rental car companies which cater to business travelers, such as Avis, National, and Hertz, but possibly less so for the companies which cater to leisure travelers, such as Budget, Alamo, and Dollar/Thrifty. You might also check some of the real off brands, such as Advantage, Payless, and since it is a colony of a European country, even Sixt. Check carrentals.com, autoslash.com, Orbitz, Priceline, and Kayak, and then you will really know where the cheapest deal is. Again though, your choices for full size or luxury suv's might be limited anyway.