I suggest a used Garmin 920XT.

Yes, that's one of the options I thought about. Even though I don't particularly like the huge square shape of the 920xt. I much prefer the 735 xt shape.
What are they going for usually ? $200. ?
Drawback is if I have a problem with the unit, with the warranty gone, it's an additional $100. to get a replacement from Garmin. Is it worth the hassle ?
Is there another option ? Suunto maybe ?

Louis :)

DC Rainmaker likes the Suunto Spartan Trainer Wrist HR for a budget option. I know nothing about it, and I love my 735XT.

Garmin 910 does all of the "basic" stuff that the 920 does. I've recently seen them selling for $60-70 on ebay/facebook. At that price even in the unlikely event that it only lasts you a year you could easily just buy another. Though if you are concerned with the aesthetics the 910 is even worse than the 920.

Vivoactive HR. Doesn't track open water swim directly, but works fine if you stick it in your swim cap or a float bag... track as a 'run' then change manually in Garmin app afterward. Super inexpensive, and has worked reliably for me.

Garmin 910xt/920xt/735, suunto spartan trainer and (possibly) the new Polar vantage M does the basics good. But the 735 is really small and comfortable, which I thinks is a big advantage. The new Polar looks similarly small and lightweight, but I would await DCs review of that before I'd make up my mind.

I recommend choosing between Garmin 735 and Polar Vantage M. Garmin 735 time-tested, and the Polar as one of the newest. The Garmin 735 is likely to have a discount on Black Friday or Cyber Monday.

This.

If you want to spend minimum cash and have good data across the three disciplines, then get a second hand 910XT.
If you don't want it because it doesn't look as nice as the newer ones or is a bit bulkier, then you didn't give the right brief in your OP.

Garmin Fenix 3 HR can be had between 199 to 250 quid these days while almost identical to current gen top tier products. Thats pretty great value imo.

If you truly dont care about any thing but a functioning watch that is reliable and gives all the data you can handle during a workout or race, then find an old 910xt like others have said. Sold mine on here 2 years ago for like 80 bucks and it was in perfect working condition.

I bought a 920xt refurb just before I sold that one (so 2+ years ago) for sub 200 bucks,so you should definitely find something lower than that now. Again, never a glitch with the watch. I only wear my watches for workouts as I have "real" automatic watches I wear daily, so I dont care what it looks like. I still have no desire to spend 100's on a new upgrade as the 920xt still covers everything I need. And I'm the type to waste money on gadgets.

Purchasing any other watch, at least by garmin, would be outside of the original description of what you are looking for. And I only think the 920 is worth buying if you have trouble finding the 910 in good shape. I like the color and GLONASS of the 920, but if I was on a budget, 910 flat out works.

I have the 920xt and have had battery issues with mine. The battery died at the 11 hour mark at IMFL last year. This year I did not start it for the swim and it died again this year at about 9-10 hours.

I don’t recommend used garmin. All of mines started to have issues around 2 years mark. Stratos 2 is awesome. Around $200. Only thing is that it doesn’t connect to power meter. Just fyi. I’m not spending more $200 after all these garmins trouble.