Natalie I also live in a comparatively cold zone and I am still fertilizing. My plants seem to be coming out of a period of no growth during the height of summer so I want to feed them to get them as healthy as possible going into winter.
Depending on how comfortable you are with chemicals and solvents and the like, BAP can be relatively reasonable. You can buy it in powder form for $1-5 per gram (depending on how much you buy). The real problem is that it isn't terribly soluble in water to start with so you would need to dissolve it in a pretty basic solution prior to adding water and a solvent like DMSO (which you can also buy reasonably). The working solution of BAP is 1:28 dilution of BAP-10 (which is a 10% solution) or roughly 3.45 grams/liter. Just some food for thought.
