How to automatically assemble lithium polymer battery?
Ask the battery supplier to provide the battery protection PCB (the PCB at the end of the battery) with contacting areas, and use "pogo pins" (i.e. "spring-loaded contacts") on your PCB. You'll then only need to make sure that the enclosure of your device presses the board onto these pins without exerting pressure on the cell itself (don't mechanically stress Lithium batteries for explosive reasons).

But really, I'd presume that, yes, the cheapest way here is hand-soldering. I don't know how your PCB ends up integrated mechanically in the end product, to be honest, and that's the step where an additional attachment action probably could happen, anyway, so I like the connector idea – especially since batteries with connectors are produced in large quantities, so you could benefit from economics of scale and don't come out that much more expensive.