Every time we change water in our tanks, when we are using CO2 injection, we are adding high pH water to a low pH tank. There will be nearly a 1 pH difference between the added water and the tank water. Many of us do that, and never see any ill effects at all. In fact water changes done that way sometimes stimulate the plants to do a growth spurt, and the fish clearly enjoy swimming in the new water.
Have you considered buying one of the whole house water filters, that uses a carbon filter plus other filter or filters to remove things like sulfur from the water? That should be less than $100 for a good filter assembly and the filter will last for hundreds of gallons. I use one on my continuous water change system, which as I recall only cost me $25 or so. I do use a very low flow rate thru it, which isn't the same as doing a big water change with one, but the idea might work.