I've gone through the same thing and can't afford a gallon of the expensive treatment so here is what I've found also living in Florida:
I try not to water so late in the day that plants can't dry off.
The organic 3 in 1 sprays can work. I hold plants so under leaves can be sprayed too.
Right now I'm trying that "Green Magic" process and that is promising in controlling rust. You can get a gallon off Ebay for $20.
(Simple Green is not the same, it has to be "Green Magic") Use 4 oz per gallon for 1st spray and 2 oz per gallon each week after.
Rusty plants are cut back prior to 1st spray for effectiveness. I also use Green Magic in a spray bottle to hand spray under leaves of rusty ones.
Also (although I'm not a fan of the Bayer Company) the Bayer systemic fungus spray does work and I think that is about $16.95 per quart.
I have all my rusty plants in a "rusty row" single file for easier treatment. I try to buy only plants with a good rust rating although I have some well-known that were traded to me that have a rusty line, so I may not be using those in my crosses.
Nitrogen flames rust so using high N fertilizer may not be a good idea. Fertilizer with a high last number are better at retarding rust. I also use soil mineralization to make plants stronger. "Ocean Solutions" is good to use, but I don't like the high shipping charge; may break down in the near future and order some more since I've not found anything that really replaces it.
I've been told to soak new plants in Green Magic solution for 2 minutes upon receipt. Haven't tried that yet.
Rust here came INSIDE plants from a well known NC seller (Not Blue Ridge).
Plants I got from Tink were clean, but rust spores abound everywhere.
Wynn Daylilies uses some kind of $500 a gallon spray and plants I got from there have stayed clean. It also depends on how rust resistant plants are. I have plants here that have totally resisted rust thus far.
