(Note, my building is actually 3 phase 208 volt not 240volt so I don't have 240 volt plugs but 208volt plugs)
But really, doing a subpanel yourself to expand breaker capacity is a really simple project - most people if so inclined could do it themselves. Anywhere from $100-200 for the panel itself depending on how many spaces you feel like adding, up to $80 for a large enough breaker to feed it, and some tens of dollars for SER cable.
IMO, what usually drives up the price is the ancillary stuff - opening up a wall (and re-finishing it) because there isn’t enough physical space, or adding extra main panel capacity/service capacity because the main feed is insufficient, or having to run heavier than expected wiring because the only available space gets really hot (poorly ventilated attic space), or having to run surface conduit due to a specific challenge with framing.
Then add in labor (where I was in a high cost of labor area), and it can get expensive quick.
An actual surface mount subpanel and appropriate wires/breakers is usually only a couple hundred bucks total like you note.