Inexpensive Veg*an Diet (?)... Some health issues...?

You are right, vegetarian diets and vegan diets can be healthy as long as you eat a wide variety of foods.
I also have gastritis and totally was able to get rid of the medication for it.
I don't drink milk and never have but I do consume lots of yogurt. The natural probiotics or what ever is very soothing to my stomach.
I also added chamomile tea daily, which is a digestive aid and is also soothing to a gastritis tummy. At first I drank a cup with each meal.
I had to give up ANY carbonated beverages, eat smaller portions of high fiber foods and cannot eat them in abundance either.
High fiber diets are pretty hard on a gastritis stomach so be careful there. I had to switch from my favorite crunchy high fiber cereal to cream of wheat :(
Pasta and rice doesn't bother but higher fiber grains like wheat berries and wild rice do if I eat it often.
With those kinds of changes I stopped taking Prilosec and haven't needed more than a mild antacid in over 4 years.
Good luck.

You will lack essential proteins, lipids, and ammino acids without mean.

Humans are omnivores, not herbivores.