If originating in the US, find a cheap OW to Europe (MXP, SVO, WAW) for about $350 from jfk, and then just keep doing your travel back and forth with all flights originating in europe. If you really want cost savings you can book CPH/ARN/GOT-NYC/MIA/LAX/SFO in the $440 range, though this all depends where in the US you are.

I did this strategy one spring where I was going back and forth every few weeks all summer, and it saved me a decent amount compared to buying all my tickets ex-USA