TV Video Overlay circuitry?

I need to produce a simple, very low cost product which is a TV set-top
box to be connected inline with the TV signal cable that will generate
simple preprogrammed animated overlays. The TV program image will not
be affected, just overlaid.

I have Googled this but only find add-on graphics cards for PCs which
cost several hundred dollars. I need something which can be mass
produced cheaply.

Could this be manufactured cheaply (say under $10-$20)?
What kind of circuitry/chips would I need?
How do I program the animations?
Where can I find out about this?

Could someone please point me in the right direction?

Thanks in advance.

Mitch

.