1996 Chrysler Concorde Tune up?

My Engine light came on, first it was blinking, then abut 15 minutes later it stayed on (red). I took it to a mechanic right away and he told me I needed a major tune up plus a part. Totla withought labor is about $260. By the time this is done, it will cost about $350 to $400. IS THAT RIGHT? I've known tune ups to be around $175 and this would be the most expensive tune up ever.

I would appreciate your thoughts on this.

Thank you.