Render to Texture alternative?

I'm creating an app that uses RenderTexture with the trial version of Unity Pro. I'm willing to buy the Pro version only because of this feature, but I wanted to build to Android and iOS as well.

But I just found out that this is a feature for all Pro versions, so I'd have to spend $4500 to build to all these platforms, which is out of reach for me.

Are there any alternatives for this? I know RenderToTexture Free, but I'm afraid it wont work because I need to update every frame.

My use case is that I have a camera rendering to a texture and this texture is being applied to a model that is watched by another camera. Besides, I need to save this texture from time to time, but time consuming on this is not an issue.

Thank you.