Hotspring.com offers multiple hot tub lines with built-in salt water systems and mostly four and five-star reviews. Most hot tubs can also be made into a salt water hot tub by purchasing a stand-alone salt water purification system.
The benefits of salt water hot tubs are somewhat contested, and few manufacturers offer models with built-in salt water systems. Since salt water systems can cost upwards of $1000 extra, most manufacturers offer them as an optional add-on rather than including them in the cost of the hot tub. Hot tubs specifically designed to include a salt water purification system are therefore somewhat hard to find and can be significantly more expensive than other models.
Another option is to purchase a standard hot tub listed on a site like Top Ten Reviews, and attach a salt water system to it. This opens up more possibilities in terms of both hot tubs and water purification systems, and can be much cheaper than looking for a salt water specific hot tub.
Stand alone salt water spa systems are much easier to find and can be integrated into existing equipment. Many hot tub and hardware stores sell stand-alone systems and can attach them to an existing chlorine or bromine system. These systems can cost anywhere from $100 to $1200 and are also available for order online, though the more expensive ones may require professional installation.