I still think food is relatively cheap. Valid reasons to grow your own is more to get interesting & tasty stuff thats not in the shops as it doesn't really save any money imo, as food would still have to get loads more expensive for that....
Grow you own both privately and as any larger enterprise, has to compete with the low cost of food and the low cost of the mass global transport of said food, from industrial scale automated/mechanized farming in regions with the ideal soil type climate to suit each crop. That is why any modern small mixed market gardens have to have added value (be organic/specialize in some thing unique/ have a niche) and are very hard to make any money from. Its also is why the once common historically localized - (low food miles before it was a trendy idea) market gardens, near each city and town died out. This may change in future its current trends continue though.
There is a well run local place the does veg boxes that buys in some stuff and uses voulunteers alot for free labour, sometimes run courses etc. Prices are more expensive and if if all labour was payed minimum wage it would probbaly be even more v supermarkets. I mm not extacly sure how there finacial model works but id say its more like a non profit/ charity the relies on community goodwill, and ran by people with other sources of income.
Also another more commercially run place has a farm shop thet buys alot of fancy more processed food lines along side the veg they grow. Id summarize/guess all there profit is from the stuff they buy in & that subsidized the cost of the stuff they grow. They sell posh jams etc for 5 quid a jar v lidl that sells jam for 30p a jar. 30p a jar is cheaper than you can buy empty glass jars when I looked into it. So probaly you pay more for the jar than the jam with the lidl jam.....wouldn't be suprised if the the packaging is the higher % cost of many foodstuffs which underlines how cheap the actually food is.
Also id guess why the alotment is full of the types you don't like. GYO ethos tends attracts people with "alternative" views, socialists/ hippies etc basically. Becasue they are idealists doing something the doesn't make finacial sense.