I have the CD soundtrack. It states that the budget was $4.5 million. In the USA it took in over $8 million in 19 days.

The Wikipedia page for the movie say it made 50 million which would make it one of the 10 highest grossing movies of the year. I tend to think that number might be off considering the lack of b.o. data usually means the movie did not do well.

Depends on how you define "classic" (there are terms like "small classic", "minor classic", "modern classic" etc.). As far as I know, many people remember this movie quite well; it even helped install a trend for medical thrillers at the end of the seventies.

well i always assumed a classic was well known,this movie does not have a household name

I beg to differ, billythepub, by many critics and afficionados it is considered a minor classic thriller, dealing with paranoia and dark pessimism - a typical theme for classic 70s thrillers (Chinatown, The Parallax View, The Conversation etc.).
I dont know about the budget, but I once read on "the-numbers.com" that it made about $ 30 million in the U.S. alone (about $ 100 million today, considering inflation) - so it could be considered a hit.
Anyhow, these numbers sometimes change, so it cannot always be taken for granted.
Hope that helped

i dunno if it was a hit as it's not a classic or anything,like most people in know never heard of the movie