I thought you could just use a hot water heater for the boiler(s).
Just for parts I'm looking at $1500+ easy?
When I built my 36x48PB, I was going to do in-floor radiant, and use a large capacity domestic water heater instead of a boiler. Some people told me it wouldn't work. I ended up scrapping the whole in-floor heat idea when my biuilder told me that his own building, with a similar footprint, rarely needed the heat turned on, as the ground under the slab, and therefore the slab too, will stay at about 50 deg during winter.
He used a Reznor LP for the days when the building temp dropped into the mid-low 40's, during sustained sub-freezing temps.
My building, with no heat, stays at about 50+/-. With outside temps in the 20's at night, my building cools down to 46-47. during the day, even an overcast day and mid-30's, the building is in the low 50's. So I do not think it would take much to maintain mid-50's. An 85K btu Reznor or Max would do it on the cheap. There is no doubt in my mind though, that in-floor radiant would be more comfortable to walk on and work on.