To add to Paul A’s response, if you don’t have a need for a Five speaker and don’t plan to add any conventional passive wired speakers to your system (which would need a Sonos Amp), then a Port is the best and lowest cost solution.
An even lower cost solution would be to find a used Connect. The Connect was replaced by the Port. The only issue with a Connect is that you need a relatively recent version if you are using the S2 version of the Sonos App. As far as I could establish, the later versions have serial numbers starting 1502. But to be on the safe side I would look to find one with a serial number starting16xx. Of course, buying used is always a risk and you wouldn’t have the warranty that comes with a new Port.