Street food is usually the cheapest cooked food available and often among the best. The price is explained by what the format removes rather than by what it compromises.
Most restaurant costs simply do not exist
A restaurant's price carries rent, fit-out, service staff, utilities, insurance and a dining room that sits empty for much of the day.
A cart carries none of that. Its fixed costs are the vehicle, fuel, a pitch fee and the labour of the people already standing there.
That difference is large enough to fund a lower price and a similar or better ingredient spend at the same time.
Volume spreads the fixed costs thinly
A specialist stall may serve more portions of a single item in a day than a restaurant serves plates in total, because the transaction is quick and the queue is continuous.
Each portion therefore carries a very small share of the day's overhead, which lets the vendor price close to ingredient cost and still earn.
The economics reward speed rather than markup, which is the opposite of how a table service business makes money.
Buying whole is cheaper than buying convenient
Vendors generally buy unprocessed goods: whole grains and pulses, unbutchered cuts, unpeeled vegetables, whole spices.
Every stage of processing that a supplier performs is a stage the supplier charges for, and skipping those stages moves the cost from money to labour.
Since that labour happens during hours the vendor is not serving anyway, it is close to free in cash terms and yields fresher components as a side effect.
A narrow menu eliminates waste
Waste is the hidden cost that pushes prices up, and it grows with the number of ingredients a kitchen has to keep on hand.
One dish means a handful of ingredients, all of which are consumed daily, so nothing sits long enough to spoil or be thrown away.
Trimmings and by-products also get used, because a cook making the same thing repeatedly finds a place for everything the ingredient yields.
Reputation replaces marketing spend
A stall's customers live or work nearby and return often, so quality problems are noticed immediately and cost the vendor their regulars.
That direct accountability does the work that reviews and advertising do elsewhere, and it costs nothing to maintain except doing the job properly.
The pressure runs towards keeping quality up rather than trimming it, which is why cheapness and quality sit together on the street more comfortably than they do indoors.