50k seems high, at least without installation costs. I have gotten pricing for this size also and can say I have seen pricing range from about 15k for a similar cast iron system that you linked to, to around 63k for a Clayton steam generator with various pricing in between. It seems to me that plenty of breweries have gotten by just fine with these cheap cast iron boilers but I don't know what kind of life span you will get out of them since I don't think they are usually considered good for process steam. Realize that in addition to the boiler you need a feed system, blowdown separator, and ideally a chemical treatment and pretreatment system which some quote with their boiler and some don't. Install is expensive too. You can try to do this yourself as I believe many municipalities don't require a licensed person to do this work, but I am not sure I would recommend this. For 250 gallon system though 500k BTUs should be fine. Use water for instance to figure your heatup. 250 gallons x 8.34 pounds/per gallon*delta temperature change (say 125) which is only about 260k btu's to heat in 1 hour or about 350,000 in 45 minutes. From that point you can figure your running BTUs roughly from manufacturer's specs. Say they say a strip takes 3 hours. 10 percent beer says you have 25 gallons pure ethanol in a full load. This gives you about 71 gallons of 70 proof low wines (latent heat maybe 2/3s water, 1/3 ethanol, maybe a chemist can say if this basic idea makes sense). Take a heat of vaporization necessary to vaporize this much and divide by 3 hours and you have your running BTUs (this all assumes no loses which of course isn't the case). Do the math though and you can see that worst case you stagger your startup time by at most 45 minutes and you can heatup one vessel and run spirit on the other with no problems. I have no idea what a 500k BTU boiler costs but I'd say a nice 1 million btu is around 30k, and going up in down in size usually isn't a huge or proportional difference from what I have seen. Good luck.