The LX models are built by toyota with a 25 year life span in mind. I would take it to a toyota dealer, tell them a independent shop mentioned some concern about frame rust. When they look at it and see the rust see if they will put a new frame under it for you as a gesture of good will, or perhaps toyota will buy it back. If they blow you off, tell them you were under the impression these were quality vehicles and supposed to last for years. Its a LX and supposed to be much better quality than a tacoma-which toyota has replaced many frames for under good will. If that doesn't work, put full coverage on it, and hope you crash it into a tree or something.