The boiler is the expensive part of the radiant heat system. I was fortunate because my neighbor works for a company that designs and sells to the plumbers/contractors. He got me a screaming deal on everything so there was no way I was going with a different system. You can use a water heater in place of the boiler but I'm no expert on this so I really couldn't tell you much. YouTube, on the other hand, will make you an expert in no time.
I do know this... For what cold was left after getting it running, I'm almost looking forward to next winter. Very even hear throughout the shop. Even up near the ceiling was no warmer than floor level. Unlike forced air, no real heat rise. Also, I could open my 12' x 24' door and once it was shut it was still warm. Again, unlike forced air, the heat doesn't escape in the wind. Everything in the shop absorbs the warmth and it stays that way.
Another benefit is no noise. You can't hear this running at all.
I do have another boiler that I'd make you a deal on if it would work for you. It was a little big and complex for my shop. I have a closed loop system. Depending on what you're thinking, it might work for you. I could give you the specs but you'd have to do the homework.
I didn't do anything for cooling except lots of insulation and windows I can open for a cross breeze. The shop gets some afternoon shade from the neighbors trees and my ceiling goes from about 14' to 18' at the peak. Hopefully any heat will stay up there. We'll see this summer.