Import gradients from Illustrator to AE without buying an $80 plugin?

No plugin is needed if you have Adobe XD installed. Almost everything you can create in Illustrator can be imported as shape layers, if you Create a new XD file, use File/Import to import your prepared Illustrator file, then immediately use the  File/Export/After Effects menu. AE will open a new comp with all of the shapes and gradients, and even brushes will be converted to shape layers. The only caveat is that you have to expand Gradient Stroked lines. It will turn them into filled shapes with gradients.

I quickly assembled three layers in Illustrator with complicated shapes. The bottom layer was a simple path with a gradient stroke, an AI-generated Fish layer was created from the stroke, and a goofy closed shape with a bunch of radial gradients became the top layer. The bottom path was selected, and the Object/Expand menu was used to expand the gradient stroke. I then opened XD, created a new file, imported the Illustrator file, and immediately used the file menu to Export to After Effects. I got many extra shape layers that could be deleted, but the entire file came into After Effects with no problems. If you are careful about arranging your artwork in Illustrator, you can use this technique to quickly create a bunch of shape layers that can be animated using Shape Layer animators. I do it all the time. Most of the time, I create a duplicate Illustrator file that only contains the shapes I need to turn into shape layers, and then I copy the layers and paste them into the main comp.

Here's an Animated GIF showing the workflow. I had to speed up to keep the file size down so you could see it on the forum. In real-time, it took less than two minutes to fix the gradient stroke and open the funky AI file in After Effects.

You can import an illustrator layer with gradients into AE, and as long as you don't need to convert it to a live AE shape layer the appearance will be preserved. 

The overlord pluginis the only way I have ever seen to get a shape layer (with only linear or radial gradients) from Illustrator to a shape layer in AE.

You could always recreate the gradient in AE once the Convert to Shape Layer command has done the conversion.

This is one of the reasons most users only recommend converting an imported vector graphic into a live shape layer in AE if you have some compelling reason to do so.