Home Depot has the best price for installation, but make sure you look over their shoulder and they do it right. I had new tile, water heater, and a dryer installed by them over the years. The only one of those that was installed properly was the water heater! (They didn't balance the dryer or use the manufacturer's recommendations for installing it so the heat sensor didn't work after installation. My DH had to balance it and put in the proper ventilation ducting to get it working correctly. The tiles they put in became loose days after installation on my kitchen floor!).
They contract out to cheap contractors and pay them very little to do the work.
I have learned my lesson. Next time we are going to DIY or hire someone outside the store even if it does cost more.
RPocai
BTW those Tankless water heaters are Awesome! I have a friend that has one. She Loves hers and says she will never go back to the tank type.