Hello: It’s possible to get a smaller tank with a higher btu input. Although I prefer more energy efficient models, one example is the AO Smith BT-65. It’s a conventional small commercial 65 gallon, 65,000 btu heater. That sort of sizing is the direction I’d go rather than a big tank. Use the “first hour rating” to guide you. There are smaller gallon-age heaters out there with the high btu input.
If the shut off valve is bad, it might be worth simply replacing that so you’re under less pressure to find a heater fast 😉
ps. I should add that sticker shock is likely to happen no matter what. Heater prices have gone up a bunch since the new FVIR safety rules took effect.