iMovie came with my phone but I believe it costs $5 in the app store and there are no additional fees or add ons you can get. It's a basic editor without many features or thrills.
Videorama is tricky with their pricing. It's free to use if you don't mind a watermark in the corner. To get rid of the watermark it costs $3.99. To add additional features it costs $.99 for each one, of which there are 10. For one item you can unlock it for free if you leave a review. They recently did an update where for $5.99 you can unlock everything they offer. Videorama has HUNDREDS more features than iMovie and access to free stock videos and images via Pixabay.
PocketVideo is suspiciously free and has no watermark. However, after creating a few videos it will force you to complete a survey where it asks you if you would be willing to pay for the app by features, by subscription or by a flat fee. PocketVideo has THOUSANDS more features than iMovie and Videorama combined. It is chocked full of imagery and options and it's also directly tied to YouTube. You can access the YouTube music library and any public video in case you want to do video reviews. PocketVideo is also the worst to work with and is glitchy beyond measure. Truly, all three apps are glitchy, but PocketVideo is seriously the worst. It's good for creating opening and ending titles. But for editing your video? Not really.
If you are looking for flash and dazzle and lots of gifs floating in your videos, choose Pocket Video. If you want nice effects and can spare about $10, choose Videorama. Want simple clean videos with a few effects, then iMovie is the way to go. OR, if you're a little ditzy like me, get all three and mash 'em up!