With SQL2016 you can do Basic AGs with Standard Edition.  Clustering has been possible on Standard Edition since at least SQL2005.  

I would aim to implement on Windows 2016.  W2012R2 seems very brittle compared to W2016, especially for clustering.  Also, W2016 has got some very good data replication built in to it, and can also exploit the latest Hyper-Convergence based hardware.

I certainly echo bmg002's comment about getting in some expertise if HA is new to you.  There are many new and interesting ways to make your data unusable with HA, but done right it will provide a much more resilient environment than is possible without it.

Whatever HA solution you choose, look at ongoing support as well as implementation costs.  The number of people who know AGs is large and growing all the time.  The number of people who know clustering is large but probably on the decline.  The number of people who know DxEnterprise is not many, however good the product might be.