Fist off it's millions of dollars cheaper than real gun store stuff which is getting downright ridiculous in price.
You are using some really expensive solvent. The real question is what is the cost per use, and I suspect that Simple Green costs more per use because you use lots more Simple Green than you do solvent when cleaning a firearm.
I prefer dry nitrogen to blow it out with)
which is many, many times more costly per use than compressed air . . .
e.g.- I like Butch's Bore Shine. I bought the 8 oz bottle 5 years ago, and paid about $9.00. It is still about 1/2 full, so in 5 years I have used about $4.50 worth of solvent. So, yes the solvent is expensive on a per gallon basis, but I use very little each time, so cost per use is very low (don't ask me how low, I just know that I shoot almost every week, and I clean my firearms after each trip). I clean the exterior of my guns with Hoppes #9, always have, and my 32 oz bottles last a looooong time, this one about 8 years, still about 1/4 full.
Current price for an 8 fl oz bottle of Butch's Bore Shine on Midway is $12.49, or about $1.55 per fl oz. Current price for Hoppe's #9 is $11.99 for a 32 oz bottle, or about 37 cents per fl oz. A quick search on walmart.com shows me that Simple Green (original formula, original scent) costs $39.88 for 24 fl oz, or about $1.66 per fl oz. Cost per fluid ounce is higher for Simple Green.
But we were talking about cost per use. How does it get used? I dip a brush into the bottle of Butch's bore Shine and punch the bore, let it sit, then punch it again, patches until clean, then a drop or two of Tetra on a patch for the bore. Done. Scrub the outside with Hoppes #9 on a brush dipped in the bottle, then wipe until clean, then wipe with an oiled cloth. From simple math, I can calculate that using my current cleaning routine, it costs me about $2.50 per year for gun cleaning solvents, or about the cost of 5 teaspoons of Simple Green (about 10 sprays). I have a hard time believing that I can clean my guns all year with 10 sprays of Simple Green, specifically because I clean my guns about 50 times per year.
I won't even get into the fact that I re-oil my guns with really expensive gun oils when I'm done, because my bottle of BreakFree lasted me many years before I ran out.