Dovetail Games is currently running a flash sale on a a few of the add-ons for Microsoft Flight Simulator X: Steam Edition. These include different things like plane, scenery, mission packs and more.
There are seven different bundles to choose from with the cheapest being $12.98. The most expensive of the batch is $27.20. You can go ahead and check the Steam listings to see which of one appeals to you the most.
The flash sale ends on June 1st, 2017.