In reality at 500 Euro you are going to find very few Heuer branded watches these days.

The only ones you will find will likely be from the diving watch range from the early 80's. Search for 1000 or 980. or 2000, but even then double check them against pictures online as a quick eBay search found a 980.006 with a seconds hand that was wrong and I expect a replacement movement (even though it's only a quartz, but still).

Check through the Chronotrader side of things here to see what's up for sale as you are more likely to get a fair price on here than eBay etc.