A well-known diner in Middlesex County is up for sale. The asking price for the Menlo Park Diner at 1475 U.S. Route 1 south in Edison is $4 million, according online real estate listings. The property, which lies just south of the Menlo Park Mall near Roosevelt Park on the busy highway, sits on a lot of two-thirds of an acre. The 4,500-square-foot eatery opened in 1960 and was renovated in 1968, according to records. It has 68 parking spots. The diner had been open 24 hour a day for about 30 years until the COVID-19 pandemic struck in 2020. The pandemic spelled the end of the Menlo Park Diner’…