Hi Stijn
Yep, these are pretty rare, but don't confuse that with being very expensive - at a guess, you should be paying around £600-800 for one, if in good condition. These 'budget' Heuers didn't seem to be in production for long, and that probably accounts for not many being around.

I haven't actually owned a 13-1, but I did own a Ref. 12, which is similar. It was built to a high quality, and I really liked it. The movements weren't signed, no idea why. I guess the problem with the Ref 12's and 13-1 is that they fall into a 'no-mans land'.. in the sense that they are decent quality chronos in the Heuer range, but if you spend a little more, you are in the realm of the more popular & well known 'named' chronos - like the 7750 Montreal, Pasadena etc. Spend a little more, and you are in ref. 510.xxx territory - so these ref 12's, 13-1's, 1614's etc seem to get left in the wake of the better known watches.
They are what I call 'gateway' watches into Heuer collecting!

As much as I like them, my advice, (unless it's very cheap), is to spend a little more and go for a better known model, like mentioned above.

Stewart
Heuerville