As a kid back in the mid 50's to early 60's, I definitely did not have $300 to buy a rebuilt flathead engine, however, the junkyards around Baltimore, and within a 50 mile radius, had plenty of these old engines to pick from in the $50 - $75 range. Some were tired and worn, but many were scored in great condition.
We could blowup an engine and/or a transmission during the week and by the weekend cruising the drive-in's again with a good engine/transmisson.