Complex sentence: The most basic model was the LX, with the SE as the mid priced model, a new trim named "SES" as the value model, and the SEL as the highest end model, with it slotting just under the Mercury Sable LS.
Split into simpler sentences: The most basic model was the LX, with the SE as the mid priced model. A new trim named "SES" was a slight step up, and the SEL was the new top-end model, slotting just under the Mercury Sable LS.