Unfortunately this isn't true. It's also not true if someone says you must always eat organic. Sometimes it matters. Organic can mean different things from different certifications so might need to research individual products, but one constant is that it isn't spayed with pesticides.
- Organic, whole foods, all-natural - none of this matters. You're paying more for no reason. Organic specifically is a title given to food that is very loosely regulated and means very little. A regular can of corn and an organic can of corn are all the same to your body and one costs 1/3 of the other.
Your body can only process out so many toxins in a day. There's lists out there with the worst foods for pesticide saturation ("dirty dozen" etc.). Something like a banana doesn't make as much of a difference if non-organic because you're going to peel off the part that was sprayed and not eat it. Grapes on the other hand are one of the worst and organic could make a difference. On the other hand, if you're sedentary and getting toxins from eating lots of processed foods and drinking lots of alcohol then paying more for organic grapes might not be a noticeable improvement in your health.
Broadly speaking being active and eating healthy is cheaper than not. Less illness and injury means less medical payments and missed work.
When it comes to vitamins, unless you've done bloodwork to see deficiencies it's hard to know what you're lacking. Big pharma would rather you be on their drugs so the doctors they own don't typically prescribe more than minimum vitamin related bloodwork. You might need to go to a naturopath for a full panel and pay out of pocket. Could be $300-400. But then you might be able to target your health naturally and cheaper in the long run.
Most people I see are lacking D3, various B vitamins, and magnesium. These are cheap to supplement. You can also get them through food. D3 is literally free, just go outside and get sunshine. A 20 minute walk every day fixes so many health problems it's absurd and that also doesn't cost anything.