I heard/read molasses is good for sweetening the soil, but as far as I know, that is probably it.
Hydrogen Peroxide (IN PROPER DOSES) can be extremely beneficial to your root system. It provides much needed oxygen to the roots. Also good for anti-bacterial cleaning......just be careful, can burn you or clothes easily, extremely bad in the face/eyes. Use caution. But even then, I think you need a certain strength Hydrogen Peroxide to be effective. I always go with Hydro store grade stuff. Not drug store pharmacy grade stuff.
Epsom salts can be used to supplement the plant.
"Epsom salts contain hydrated magnesium sulfate, two elements crucial to plant growth." But these are secondary nutes. Still crucial, just not your primary nutes.
But a real, fully functioning fertilizer from household products......I can't think of any.
Myself, I would just go to the store get some decent priced nutes, then put them in a non-descript bottle with a marking only you know the meaning of to distinguish them from eachother. There has to be SOMEWHERE in the house you could store the bottles out of the way of prying eyes.
I know you stated price was an issue, but the wrong home brewed concoction could really mess things up if not careful.
I hope others have better suggestions for you, cause I am also interested.....not that I would necessarily actually try to brew my own, but it is interesting question none the less.
Good luck OP