Stabilized ammonium nitrate seems the best bet so far, but manufacturing it seems virtually beyond the scope of the kitchen lab. does anybody have any ideas?

What "best bet"?

 

The only good oxidizer is liquid oxygen. Everything else is inefficient, explosive, toxic - often all at once.

 

So what kind of improvement do you seek? Shall it be solid, cryogenic, storable? First stage, interplanetary mission, lander?

 

These days many companies claim to have a magic "green" propellant and they are just crooks. Their stuff uses to be very dangerous and inefficient, but somehow they manage to get subsidies.

 

Within few years we won't need to replace tetroxide any more, because satellites and craft will all use ionic propulsion, and applications needing more thrust will have oxygen+fuel. Indefinite cold storage with a cryocooler is a better answer than all these bad chemicals. A glow plug is a better answer than hypergolic ignition.

 

I wouldn't waste a single cent on these useless and dangerous attempts, where the present generation has forgotten why so many propellants were abandoned and re-discovers it the hard way. Things like N₂O, peroxide+ethanol, acetylene are just unusable explosives.