Is $1,600 to replace gas valve on an old furnace a fair price?

I'm a first-time homeowner. We've been having furnace issues over the last month or so, starting with needing the thermocouple replaced, and this morning the pilot would not light. We called someone out, and they said it's the gas valve. When we bought the home, we didn't have much info on the furnace (no manual, etc.), and the technician today said it's probably close to 20 years or older, so the part we need is harder to get. I'm not sure if it's worth having more people come out or getting different quotes. Our home has no ducting, no A/C - just the furnace and a gravity vent in front of it for the upper floor. I can't afford all of the extra cost for them just coming to look; it's been a hard year, and our savings are already tanked from issues earlier in the year with the home. We're leaning toward replacement at this point, I think.