I just noticed that for the next 24 days (so until around the 11th of July) the 4 previous Bayverse Transformers movies are on sale for $8.99 each or all 4 for $31.99 on the Xbox/Windows movie store.

Note that Microsoft's movie service is streaming based not download so if you have bad internet this isn't for you. And yes you own it with your purchase but you can only stream it.