No idea on a budget ballpark. Other than what you spend on batteries and cables, cable lugs, regulators, isolators, etc., it all comes down to labor. Someone who knows what they are doing should be able to do the entire thing in a day, so plan labor costs accordingly.
Talk to truck dealers, making sure one is intimate with electrical issues. RV dealers (but those can be really hit and miss, some are good, some are clueless). Also, talk to a really good auto electric guy. And, if you're near the ocean or a large water recreation area, this stuff is old hat to a marine electric guy.
Greg, I agree with ya. At the Expo I talked with the IdleBuster folks. Nice folks, but the system comes standard with a 30amp battery charger, with a 90 amp charger being an available option. Wow. That's where, when you talk to guys dealing with marine electronics, alternators, generators and batteries, it's hard to find a system that's less than 150 amp in the alternator. It's the same as what we do. I just don't know why the trucking industry is so far out of whack.
Slow and steady, even in expediting, wins the race - Aesop