Best GMT under $800?

Not sure that it’s better but the Borealis Seastorm mk2 is one I’m eyeing up. 

It’s got a sapphire crystal and I like the clasp on my Sintra. It’s also slightly smaller than the Seiko. It does use a Seiko movement  A little over €650 so it’s within your budget. 

Someone's gonna say it eventually, so I'll be first: have you checked out Long Island Watches Republic model yet?

Just a dash over budget, but good specs.

Squale makes one too, but the blue sun burst GMT is not close to your budget. This one is kinda: Squale GMT.

If you don’t mind homage type watches, the Squale GMT is about $800

If you don’t mind a busy dial (and quartz) the Citizen Nighthawk is about $200

Get the Seiko 5.  I love mine!

This is just about the hardlex: I have had my normal Seiko5 sport for about 3 years now and I've never had a problem with the crystal. No scratches whatsoever. also I didn't really get into watches until a year ago so I wore that thing daily for 2 years. 

Visited a friend today that has the new GMT and has had the Seiko 5 sport for the same time as me and he told me he isn't wearing the sport anymore just because of the GMT. Also the Bracelet looks really good for the 350€ he paid for the watch. 

Im trying to say you won't regret buying it I think 

Not exactly gmts but the digital ones have a world timer. Plus I'm pretty sure you can set the top subdial to a second time zone. 

Lots of titanium and sapphire options from Citizen. 🙂

I own this one and I recommend it without reservation. 

TLDR Best bang for the buck look at the last link..
 
I have to go with thesharperthebetter and say Marc over at Islander Watches has one of the best offering for an affordable swiss GMT you cant beat that price for value IMO.

Islander Republic (the one I mentioned above)
https://longislandwatch.com/islander-republic-swiss-automatic-gmt-watch-with-blue-dial-isl-139/?_ga=2.89779739.1043276028.1667615239-143637611.1658681548

Phoibos $200 Quartz GMT
https://longislandwatch.com/phoibos-px023b-watch-px023b/?_ga=2.96651423.1043276028.1667615239-143637611.1658681548

Squale $825 Swiss movement 
https://longislandwatch.com/squale-1545gm-cer-bk-gmt-watch-1545gm-cer-bk/?_ga=2.101392385.1043276028.1667615239-143637611.1658681548

Aristo $200 Quartz
https://longislandwatch.com/aristo-3h80gmt-watch-3h80gmt/?_ga=2.101392385.1043276028.1667615239-143637611.1658681548

LumTec $500 Quartz (I personally love this design I just wish I could get it in a smaller case to fit my wrist)
https://longislandwatch.com/lum-tec-combat-gmt-dual-time-watch-with-a-curved-sapphire-crystal-combat-b45/?_ga=2.57876778.1043276028.1667615239-143637611.1658681548

Graf Zepplin $180 Quartz
https://longislandwatch.com/graf-zeppelin-7642-5-gmt-watch-7642-5/?_ga=2.57876778.1043276028.1667615239-143637611.1658681548

Glycine Airman 42 GMT $350 (Jomashop) 
If I was buying a GMT today this is what I would buy if I had the wrist size to wear it. It comes in several different colors ect.
https://www.jomashop.com/glycine-watch-gl0069.html

I was going to say Steinhart myself.  Solid watches for the money.

I own a glycine airman.. great watch

I think the island watch is a nice watch but it's way overpriced. I own a lum tech it's also a great watch however this particular one that you show the link for is frankly kind of ugly.

Just my humble opinion. 

Check out the traveller's GMT / jumping hour Miyota 9075 movement in the sub-$700 #bulova Wilton GMT, $475 #zeppelin Atlantic 8468-1 or 8468-3, or for a little more, the #jackmason Strat-o-timer. 

The Zeppelin is only available on aftermarket sites (Chrono24, eBay) as it has so far been low volume. It also has mineral crystal. 

The Batavi Geograf goes for $689 at full price. Pre-owned you might get it for less (here's a listing for $600 you could bring it down to closer to $500):

Similarly the Batavi Kosmopoliet GMT goes for $719 at full price (might could snag it pre-owned closer to $500}