Lowest price to date has been US$29.99. PC only. Redeems through Steam. Metacritic 88. Worth a buy, though more than likely it will be lower on Black Friday 2018. The Humblebundle store also has the base game on sale. On the Xbox Store, this and all the XCOM 2 game/DLC are also on sale for similar prices.
Note that this will be lower also if you have Humble store credit from buying other Humblebundles or have used the store and opted in to the 5% rebate. Buying this will also give you 5% back for future purchases if you click to opt in.
Edit: I think the price is $29.99 but shows as $26.99 for me as I have a Humblebundle Monthly subscription which gives me a 10% discount on the store. Still matches lowest price to date.