The only Glock magazines that I have found that are as dependable as Glock handguns are those made by Glock and ETS. I understand price being important but when a magazine messes the bed just when you need it the most you will most likely not be wishing you bought a cheaper one.
If you have to buy cheap mags use them on the range and buy a few good ones for personal protection (HD, SD, and what you keep in your car/truck).
Even now, buying quality mags, you have at least 4 months 'til November, if you buy just 2 quality mags a month you will have eight high cap mags you can depend on. That will give you 240 rounds, almost 5 boxes of ammunition, to fall back on.
Also be careful about buying mags on e-bay or as police turn ins. Makes no sense to save a couple bucks on magazines if it turns out you have to buy new springs to put in them.
Good luck in your search!