The RX has been through 2 generations and multiple sub-models.
The first generation lasted from 1997 until 2003. The engine options were an inline 4 or a V6. The first model sold in the United States was the RX 300. It was offered with front or four wheel drive when it rolled into the dealer lots in 1998. This vehicle sold like hotcakes because it was cheaper than SUVs from other luxury manufacturers and it was loaded with luxury options like heated exterior mirrors and premium sound.
A Coach Edition RX 300 made its debut in 2002. It came with a Coach leather interior and many upgraded options. These were limited in quantity and demand a premium on the used car market.
The second generation started with a restyling in 2004. The new RX is much sleeker than the original. The V6 engine options have also been upgraded to more powerful beasts to match with the 5 speed automatic transmission.
The RX 400h is the first hybrid SUV in the world. It was first sold in 2005 in the United States. It gets better mileage and has lower emissions. In 2007, the RX also got a mid-cycle restyling with the RX 350, which is different from the RX 300 both inside and out.
These cars can be found on the used market, but Lexus drivers do tend to hold on to their cars for longer than your average Chevy driver. Their reliability means they won't fall apart for many years. Still, some luxury car owners like to upgrade every two years, and their used cars end up on places like eBay, where you might be able to pick them up cheap.