LONGECITY

NAC is cheap and good if you are vegan/vegetarian (low cysteine diet) or regularly consume some alcohol.  If you eat meat and don't drink to excess, dietary cysteine should be adequate.  

Quality NAD+ & Resveratrol can be expensive.  Don't know if you're going to get the bang for your buck with these at your age.  

If I were looking at cheap/basic supplementation, I'd go with a cheap (drugstore brand) Vitamin C, B-Complex and D.  Lower dose (per pill) of these would be quite economical.  

I take a RitAid brand Vitamin-C (500mg) and their low dose "B-Complex with B-12". 2000IU of D/day should be adequate.  

Vitamin-C helps recycle spent cysteine in the body, so this may allow you to drop the NAC.  

An "FOS" (fructooligosaccharide) "pre-biotic" is much cheaper than an expensive probiotic, and may accomplish much the same result.  With so much emphasis on the gut biome these days, a minor investment here might be cost effective for better health.  

If you're looking specifically for a longevity supp, it's hard to be economical in this category, but I really like curcumin as a stand alone longevity tonic.  The "Curcumin-95"  or "C-3" formulations are the most economical enhanced absorption supps I know of, and one of these a day (take with your fattiest meal of the day) would probably be sufficient.  

Hey!    I need to cut back on costs for sure,  and have researched this a little.  So....here's what I would add to the helpful comment above:   first off,   look at diet and figure out where you would even NEED to supplement.   People sometimes turn enjoyment of life and eating into a tiresome listing of all the supplements they take for "dinner."    You may not even need some stuff that others do.   Spend your money on FOOD first.  Then,    think what YOU would need to supplement.   Save up for the big dogs in the future rather than getting possibly useless supplements now.  Lots of people on here note that magnesium and D3 and K2 are important -- these fortunately are found quite cheaply (Swansons and Now are possible formulas as is Bone Builder.)   I don't know if any of them make a damn difference but I used to run,  am thin,  and as a female I worry about bone density problems.  Fish oil is also not that expensive --  I simply drink Flax oil in a swig before dinner.  

  I also get supplements in powdered form from BulkSupplements  (I do NAC because I used to drink vodka for breakfast,  lunch,  and dinner).   I also got the alpha lipoic acid powder.   Some of the powders from BulkSupplements are very expensive,   but occasionally they also do free samples with purchase which is fun.   Be forewarned that you'll need to figure out HOW to take powdered forms if you don't like shakes,  because some of them are VERY acidic.  

So:  in sum,   Fish oil,  in any form.   C and B complex.  I'd skip the pricier ones,   personally.   Alpha lipoic and carnitine formulas.  Magnesium and D3 and K2.    I try different ones each time,  but there is no point buying an overpriced supplement.   Save up for future BIG treatments like growth hormone analogues or epithalon. 

Would say go for the most common deficiencies: http://www.longecity...-mineral-stack/

Vitamin D is probably what I would stick with if I had to pick one, and just eat plenty of nuts seeds and greens otherwise. If you can add another, do Krill.