I use and would recommend the Pinpoint II Oxygen Monitor. I have used Hanna and Milwaukee mw600 meters in the past and liked them other than they were hard to get all at once. I needed to order the probe, meter, cable, electrolyte and calibration buffer separate and not assume they were all included when ordering a meter. The Pinpointt II can act as a continuous monitor but I don't feel it's needed more than a few hours now and then to check how any changes might be working different than thought. I still prefer to rely on pump failure and low flow alarms to alert me in time to get back up oxygen to the fish.
What kind of budget were you looking at for a O2 meter? The Optical Dissolved Oxygen meters are very nice....
I don't know. Haven't done enough research to decide my budget. Something around $200 would be cool. But if it ends up costing more than that, then who knows? Send me a link :)
Not too far out of your price range.... Amazon has it for $1,278.40 with prime shipping!
I keep checking alibaba, but so far haven't found any cheap knock offs yet.