If you fly often, this limited-time sale on a lifetime subscription to Dollar Flight Club is pretty amazing. You can get Dollar Flight Club’s Premium plan for just $39.97 (reg. $690) or Premium+ plan for $59.97 (reg. $1,690). While you get these subscriptions forever, you must order by January 28 at 11:59 p.m. PT to get these prices. Both plans get you flight deal alerts from up to four home airports. This means you let Dollar Flight Club do all the research while waiting for the good deals to roll into your inbox. This includes international and domestic flights. If you opt for the Premium+ p…