Do you have a CAD model of the part done that you could share?
3" to 3.5" is not what I would call "shallow", unless I'm misunderstanding the depth requirement. I'm imagining a pie pan turned upside down. How much of a flange at the base are you needing? If this is going to be used to see through then your mold surface quality will have to be like glass. Otherwise you will pick those imperfections up from the mold and it will make your lens look like a mirage.
How many are you looking to get done? I might be interested in the project.
Thanks,
Andrew