Here's a thought on something I frankly haven't done yet but soon will try. If you see steam rising, it will be coming out the ears of purists.
Home hydroponics is populated by many people who revel in arcane real or pretended knowledge, smatterings of facts gleaned from articles aimed at commercial growers, and claims of absolute knowledge they don't really possess and which really don't exist. Many are highly experienced and have carefully tried everything. The problem is knowing which are which and if our own experiences will match.
A number of people have experience with Miracle Gro, plain and tomato formulas, and have had good results. Even some of the dogmatists have been moved to admit that Miracle-Gro has worked in Kratky and related methods. What you're doing isn't so distant from Kratky in principle.
Manufacturers cannot be expected to explore cheap options. They make their money promoting precision as a requirement. They're after fighting brand loyalty. Makes you wonder how those poor plants get by in the ground. They will tell you that soil lets plants seek out their nutrients, which I agree with, but the nutrients still must be present, and how many people are doing constant analysis to insure that?
All I can say is that I see people reporting as good results from plain Miracle-Gro as with special hydroponic nutrient kits. Who to believe? Well, it falls within the bounds of plain critical thinking, which begins with the first principle of not necessarily believing anyone who stands to gain from you believing them. So I appreciate all the efforts of the hydroponics makers, one of which owns, via a subsidiary, Miracle-Gro. And I can't expect, therefore, Miracle-Gro to promulgate anything favorable about Miracle-Gro in hydroponics. They have their own proprietary home hydroponics system to sell.
Nor do I accept the pontifications of those who immediately refuse to consider that Miracle-Gro could work at all as they toss around their scientific notions of why. And with the wide variety of hydroponic nutrient formulas floating around and all the DIY recipes, who can say anything so certainly. Humans adopt and defend intellectual territories as vigorously as geographic territories, so belief offers a different benefit to dogmatists.
The point is that Miracle-Gro is cheap, and people have found it to work, sometimes better than their "official" hydroponic" kit. It would be too much to say Miracle-Gro is superior to "real" nutrient products, but it's clear that, short of blind belief, there's no clear and convincing reason to think it can't work.
Now, Miracle-Gro may have no pH buffer, but pH Up and pH Down are very cheap, considering the tiny does used, and a working pH meter is like wise cheap. Many "real" hydroponic products also require you to manage pH. It's no burden. And you don't know if and how much you will have to do until you see a particular nutrient formula interacting with your water.
In your case, cost is the question, and it would be nice if you didn't have to mix your own from scratch. Obviously, Miracle-Gro wins in that category. I read correspondence from someone operating Dutch pot, and she said once she tried Miracle-Gro, she never went back to spending money on pricier stuff. She used it lightly and fiddled until she settled on a concentration that worked for her.
I'm building a outdoor Dutch pot set-up large enough to try a number of vegetable varieties, and I am going to go ahead late summer and see how Miracle-Gro works in it. I'll also be converting my back porch Kratky rack to Dutch pot after that, and I'll still have some hydro nutrient to use up, so we will see.
I think it's worth a try, or I wouldn't be trying it. If it works, fine, It obviously will work, the question being how well. And trying it is the way to find out. We don't have the kind of controlled growing laboratory environments that made early hydroponics so attractive to plant scientists who needed rigid controls to get their work peer-reviewable. Maybe it won't work well. Maybe I won't be able to tell the difference. But I think we have pretty good ideas of what we expect of our plants, and if those expectations are met, it's a success.
