The Chevy Monza was a huge seller for GM in the 70's. Unfortunately they had a rust problem and it is hard to find these cars in driveable condition.
The collector market for all things Monza is quite amazing. The 1975 hot wheels sell for between $20 and $200 depending on color and condition.
The rarest which is also rare for any hot wheel, is a Christmas edition given only to Mattel employees. Only 200 made.
One came up for sale this week. sold for $2280. I would have bid but I thought the $8 shipping was just too much.