So $2400 per year for them to do it. A BRS 6 take RODI system costs $350. You can get a three 55 gallon Brute Trash Cans - one for RODI water storage, one for mixing and storage of salt water, and one for taking out the water from the tanks. The trash cans on casters will set you back $600.
What I do is take RODI water and put it in my salt water can. I put in my salt mix and I have power heads in the can to mix the whole thing. When it is time to do a water change, I wheel the empty can to the tank, I siphon off about 40 gallons (I have 44 gallon cans). I also wheel over the salt water can (I have tile floors so it is easy). I pump in the salt water (which is matched for temp, ALK, and salinity). I wheel the full can over to my sink and use the pump to pump it down the drain. I wheel the salt water can back to the mixing station. I pump in RODI water (and get the RODI water going to refill the can). I dump in salt and turn on powerheads and heater (if needed). I get good mixing of salt in 24 hours and if I REALLY HAVE TO, it is probably good to go in about 2 hours. The whole process takes an hour And most of that is pumping and stuff which means it I can do something else as long as I stay alert.
So you will also need a pump and some powerheads and maybe a heater and some hoses and probably extension cords and power strips —- but all that will be had for $300 easy, So all in $1300 or so (your use may be higher or lower). But say you are doing a 50 gallon water change per month, you are doing 600 gallons per year. At say $.50 per gallon, your year outlay will be $300. So you should come out ahead of the game before a year is out. Plus, you have water on hand at all times if you need it and the ability to make more.
And sometimes being able to do a series of water changes in a short time can solve problems in your system or at least buy you time. Yeah it is brute force but brute force can work really nicely.
The downside is it takes you time and maybe you are fine with paying someone else to mess with the whole thing.