[PureHarvest]

If you do the hydro-gardens ferts, you will need 3 injectors.
One for the tomato formula+mag sulfate, one for the calcium nitrate, and one for your pH adjuster.
The dosatron 14 gpm will run you $360-400 each depending on where you buy.
Then you will need pipe, fittings, a screen filter, and pressure regulator.
And then you will need a ph/TDS meter to check your work.
Then you need three 5 gallon buckets or rubbermaid trashcans for your 3 concentrates tanks.
You would make a concentrate of the 3 ingredients and each injector pulls from each tank to mix into your water line. Ideally you would have 1" pvc water line coming into the pressure regulator and filter side, the injectors would be plumbed in series next with threaded union fittings, then you would exit to a barbed fitting to your tubing. You could also exit to a plastic manifold that has irrigation solenoid valves to run to different zones. The valves would be wired to a cheap lawn irrigation control box to control when and how long each valves would open up. The rate of fertilizer is controlled by how you mix your concentrates, and how you have the injectors set.
So, you are approaching 2k for 18 plants.

The easier solution would be to get a big tank, tub, or IBC tote and make a master solution.
Basically, you fill your container with water, add each ingredient one at a time while stirring or agitating with a submersed pond pump.
You then have a large reservoir of already mixed diluted solution to send to your plants.
Hook your tube to the pond pump, and drop it into your tank and pump to your plants.

Lots of cheap ways to do this.

A five gallon bag with two plants will need roughly 2 gallons a day when mature.
So your set up will use 36 gallons a day.
You can get a 250 gallon IBC tote around here for around $100 or less.
Cut the top off it so you can access it easier for fillin/stirring/and cleaning.
Then you will only have to make fertilizer once a week.
Pond pump under $100
pH/TDS meter varies from $100-300
5 gallon buckets 3x$5=$15

So maybe $400 if you had to buy everything new.
Much less if you can find stuff on craigslist, or have stuff on hand.

You could plug your pump into a $10 digital timer to go on and off the same time everyday. You would manually run the system one time to see how long it takes to give the volume you need. You want 10% of the total volume to trickle out the bottom of each bag when you water. Once you know how long this takes, set your timer accordingly for each day.