I'm not sure, actually. The boiler was already here when we bought the house and I haven't looked into what they cost. I did have to re-do the plumbing, valves, pumps, etc. because it wasn't done quite right and I had to add another loop when we turned the old garage into an attached suite.
The cost of all that stuff was around $2000 CAD. That was 2 pumps, a bunch of 1" copper, a mixing valve, various manual ball valves, enough baseboard heater sections to go around a 19' x 27' room and various odds and ends. Pretty much everything except the boiler. The in-floor plumbing in the garage was also already here, so I don't know what that costs either. In any event, I'm guessing the boiler at around $2K, and given that you would have more plumbing than I had for the suite, $4K US doesn't sound totally out of line, although maybe a bit higher than I might have guessed if that is just for parts. If that is total price to get it all done by someone else, then it probably isn't unreasonable.