That board is wave soldered, not reflowed. The through-hole parts are inserted from the top, the SMT parts are glued down to the bottom, then the bottom of the

That board is wave soldered, not reflowed. The through-hole parts are inserted from the top, the SMT parts are glued down to the bottom, then the bottom of the board is dipped in a fountain ("wave") of molten solder. The solder blobs are normal for wave soldering followed by hand soldering of the wires. Production costs can be very low, you just have to select SMT parts that can take the heat and thermal shock.