phoebe Wizz Air operate out of Gdansk making it by far the cheapest entry.
low cost airlines operates from any Baltic airport. Bus ticket Gdansk-Kaliningrad is same price than Tallinn-SPb or Riga-Pskov. Airline price depends from where you travel. My airport is Oslo and it's often similar prices on cheapest tickets be it to Gdansk, Riga or Tallinn. Only the way by Kirkenes to Murmansk is more expensive.
Similarly cheapest rates to Gdansk, Riga or Tallinn are sold from German airports too.
the point with the route by Mamonowo is that this border is quieter, and the ride is very short.