Canada tire used to sell evapo-rust, I see they don't any more (at least in Ontario). They have POR15 rust remover (1 qt for $14) and Blaster (1 gallon $48). I de-rusted the inside of my gas tank using several gallons of "cleaning vinegar" (which is 10% acetic acid) and electrolysis (running a current between a floating electrode and the tank wall). Cleaning vinegar, even at 10% (twice the strength of ordinary vinegar) will take a while but if you're not in a hurry and can leave the parts in a bucket for a week then that's going to be the cheapest way. 2.5L cleaning vinegar sold at the grocery store can be 4-5 CanBux.
White vinegar is I think the same strength (5% acetic acid) as pickling vinegar. Cleaning vinegar is 10%. I use cleaning vinegar instead of carpet cleaner in a Bissell carpet cleaner when cleaning my (home) carpets.
I've tried citric acid, I bought a large-ish bag off amazon almost 2 years ago (you can't buy it useful quantities at retail) you have to mix A LOT of it into water to create a concentrated solution, it's not cost-effective and it's a weak acid. I did an electrolysis test on a rusted lawnmower blade comparing 10% vinegar to concentrated citric acid - the vinegar worked better.
I bought a pint of molassas but have never tried it. I'm not sure you (or I) can buy molassas in useful quantities at retail in Canada. There's 2 different molassas I think, one is expensive (used in cooking?) and one is cheap (used for horses?). They say that Evporust uses molassas as a chelating agent.
I don't know where you can buy phosphoric acid in 1-liter or 1-gallon quantity at retail in Canada (or really in any size).
Muriatic acid (pool shock, aka HCL hydrochloric acid) might still be commonly available in 1-gallon jugs, not too expensive, I have one or two of those, but using it to de-rust is questionable. Yes it will work but will also eat your part and leave the surface in a brittle state, also you'll get flash rusting when you wash it off. It will stink and give off fumes.
