Infusion seems to be the way to go, but you only get one finished face with peel ply texture on the other. What's the best way to get 2 finished faces? I tried a small 150mm square by just clamping 2 peices of aluminum tooling plate together and it worked perfect with really good fiber to resin ratio, but I need some larger 500x500 plates (2mm thick). I could use 2 plates of glass backed up by something else like mdf maybe, but I imagine just clamping around the outsides is not going to squeeze the middle well enough unless I get tricky with the clamping. Maybe some thick peices that span across with clamps on outside to hopefully put enough pressure in the middle. 
Any other good way to do this other than clamping? If clamping is the best option, what's the best choice of clamping plate material and method for doing it? 

Pretty easy to make a solid foam core infusion ready, but it does make them heavy. I've played around with this a far bit. To get good wet-out, you need to punch holes at 2" centers, and lightly grooving the tool side will help avoid pinholes between the holes (this only needs to be as much as a light score with a flathead screw driver). As with all solid infusion cores with thin skins, you will get some print through.

It does come out somewhat lighter than Soric, but there's negligible difference between this and 3D PET core (at least in thicknesses up to 5mm), which makes it somewhat pointless given the effort. I cant remember the exact numbers, I posted a thread on here about it a couple years ago. From memory 3D PET core consumes about 300g/m2 per mm thickness, drilled and scored foam core is 295g or so. Heavier than a 2-shot process anyway. 

Corecork is still the lightest infusion core I have used at about 190g/m2/mm resin uptake. But has less compressive strength than other cores.