I think I've heard from somewhere that there is a citric acid product that is somewhat effective on rust, but nothing in our experience beats Oxalic Acid.
Get the MSDS sheet on the Clear Pink Stuff, it will provide you with the active ingredients. I'd be surprised if Oxalic isn't the main ingredient.
If Oxalic is the main ingredient, it is far much cheaper to purchase a 50 pound container from your local chemical supply source. 50 pounds will make 80 + gallons of rust remover for you. I've never heard of anyone spending more than $90.00 for a 50 pound container of Oxalic acid. Last time I purchased some here locally I believe I paid about $55.00, maybe more with tax.
But you need to take extra PPE precautions with any Oxalic acid product. Very toxic substance. I (we) use respirators, chemical resistant gloves and goggles when using and/or mixing the product. Also, when mixing the product, the crystals take a long time to dissolve. Best using warm to hot water and a lot of mechanical agitation (paint mixing attachment and a drill is what we use to mix-up 5 gallons at a time).