If it's factory EFI you are looking for, then they are a bit hard to find, & usually are not cheap when you do find one. Patience here, really is a virtue.
The purchase price can easily be the cheapest part of the deal too, particularly if you need to buy a computer & also overhaul everything before installing it.
If you are using a GX head, then the ports in the manifold are smaller & to open them up to match may involve some welding on the runners so as to have enough metal to open into. They should work with the slightly smaller ports in A14/15 heads though.

You also need to be aware that these manifolds seem to have a habit of developing a crack in the mounting flange & port area of the first two runners. This one has cracked all the way & will need surgery to repair it. Providing additional support here would be a good idea too.
You can also see the port mismatch using the gasket marks as a guide & this was on an A14/15 head.
Are you SURE you want EFI?