We get a little better than 15 gallons per filter. It comes down to about 75 cents a gallon and that’s cheaper than buying it.
I’m north of Houston in a Municipal Water District.
How much does this system you have costs?
They do not have my model anymore, but it is similar to the RD-102. Link below.
If you do an online search for Water General RD 102 you might find a decent used one on sale. Can then buy new filter replacements for it. And the water tastes very clean. Similar to distilled water which meters 0 ppm.