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There's another seating option for trips on UA metal - Economy plus. It's just another 3 - 5" of leg room, no different service, but that can be significant. It costs close to $100 for a TATL, so for two people, rt, the cost would approach $400. There's something called Annual Option, good for a year for the holder and one companion on the same reservation for $425. If somewhat better seat assignments are worth it, and if you'll be making more trips on UA, this might be worth a try. From UA's WWW site:

Economy Plus annual option
With an Economy Plus annual option, you can stretch out and relax in seats located at the front of the economy section, whenever you fly United for an entire year. Economy Plus seating can be reserved at the time of booking, if available, for you and a companion traveling under the same confirmation number. The price of the subscription will pay for itself after just a few trips!
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425.00 USD

There's a lot of restrictions on use of this option - you have to have the pass at the time of booking and flying and credit miles to UA's Mileage Plus, so before booking this, I'd call UA and ask if the Annual Option would cover your trip - it should but call to confirm that. (if you had flown a lot and gotten Premier Status on UA, then you'd be eligible to use E+ as long as you had Premier status at the time of flying, while the Annual Pass says it's more restrictive, you need to have the pass at the time of booking AND the time of flying. I think the restriction means at the time of booking the E+ seat, rather than booking the flight, but best to check on this.)

Happy travels