Let's start with some facts and figures

409 by the Beach Boys came out in 1962.

Gary Usher was probably the biggest influence over the authorship of the song which describes the car as having "dual quads" (dual quad-barrel carburetors) which were first available in the 1962 model year... so we're talking about a 1962 Chevy Impala 409.

That's a good thing, because Beach Boys fans would have had a hard time laying hands on the 1961 Super Sport 409s... just 142 of those were made.

The 1962 model year was a much bigger run: more than 75,000 were built with an MSRP of about $3,026.

So, we're looking at $3,026 in 1962.

Minimum wage in 1962 was $1.15/hour so our 409 represents 2,631 hours of work or about a year-and-a-half of full time labor at minimum wage. Of course, not everyone made minimum wage. A beachboys fan starting his first union job could expect to make rather better money, especially in a big city. Helpers and Laborers in Building Trades unions could expect as much as $4.20/hour in New York City with pay bottoming out at $1.56/hour in Charlotte, NC.

At NY rates the 409 would represent just 18 weeks wages... before tax, of course.

By modern comparison, a 2020 Chevy Impala has an MSRP of $31,620. Current US minimum wage is $7.25 so that represents 4,361 hours of work or just over two full years of full time, minimum wage labor.

So, at the time the Beach Boys sang it, a new Chevy Impala 409 muscle car was more financially accessible than a Chevy Impala sedan is today.

Edit: spelling