Just mix your own solutions. Dirt cheap and easy to do. Startup cost is very low as well. Can easily reuse your old RM fert bottles and just add whatever you need to your arsenal. Best idea would be to make a custom macros mix tailored to your source water and plant uptake but also have some normal stuff like K and P do spot dose as needed while getting your numbers exactly right. Micros too, of course and you can go rich or lean in iron based on what you want out of the tank.