Originally Posted by
redadeco
The price jumps up by $300.
Actually, it doesn't. If you can find I class inventory it will not change the cost. If you are seeing +$300 then it is because you are not booking this I fare and instead the LAXMIA segment is probably booking into D.
Speaking of fare details, the lowish price of this is due to the LAX departure, the SEA OJ on the return only adds cost. If you do this as a RT to/from LAX it can be had for $711. A little bit of ITA matrix (and reading fare rules) goes a long way to helping shed some light on what Google Flights might kick up for a certain date.