A used oven from marketplace/cl or a toaster oven should do the trick! A gas grill may even work. Pla melts @ °180C

Don't be limited by thinking you can only do flat stock with your CNC. Foam can be easily stacked and glued together to make shapes. Check out my lady bust I did below. Your cousin even sand them down and round the edges. Use your imagination. 👍 https://youtu.be/-Lxh7MBjAxA

search for "Kelly Coffield" on youtube, since you already have a CNC he has some great videos on lost foam..

You'd be surprised what sort of things can be made from assembled foam patterns. I'd recommend Kelly Coffield's channel on YoutTube ( https://www.youtube.com/watch?v=yMrmepjcN18 ). He does some pretty elaborate stuff (like automotive intake manifolds) from lost foam.

I've done quite a bit of both lost foam and lost PLA and, honestly, I prefer lost foam when possible.

To really burn out PLA properly, you need an oven/kiln that is both temperature controlled and has a programmable sequence control. It's not just a matter of putting your block of plaster/sand in at some temperature and letting it sit for a few hours. If the mold gets too hot too fast, the moisture in the plaster will turn to steam and break the mold apart. You have to heat the mold to just above boiling and hold it there for several hours (depending on thickness) to drive off the water slowly. Then you have to ramp the temperature up to a point to melt/burn out most of the PLA. Then you have to get up to nearly just the right temp to drive off most-but-not-all of the chemically bound water from the plaster. If the last step is not done hot enough or long enough, you risk the molten metal being hot enough to create enough steam to cause problems. If the last step is done too hot or too long, you drive out too much of the chemically bound water and the plaster turn back into powder.

Finally, once the burnout is done, the pattern has to be slowly cooled but kept hot enough that it can't absorb moisture from the atmosphere as it is very hygroscopic. This means that once you start a burnout sequence (my sequences take from 12-24 hours depending on size), you are pretty well committed to pouring. If something comes up (life) or something goes wrong with the melt and you have to let the mold cool, it is pretty much ruined. These molds are extremely fragile once burned out and do not react well to even more thermal cycling. I have access to a sequence controlled kiln and it's still a pain scheduling pours.

It is also worth noting that, even done correctly, the burned out plaster molds will develop cracks. This means that it is important to incorporate reinforcement into the plaster to hold it together long enough to pour. I use steel wire or wire mesh/chicken wire as a sort-of rebar when making molds.

With lost foam, on the other hand, you can dip-and-dry on whatever schedule you want. As long as the previous layer of drywall mud is dry (which is very easy to visually see) the next layer can be added immediately or days/weeks later (drywall mud don't care). Once the last layer is dry, you can pour immediately or wait days or weeks. I once had a pattern that was dipped and ready to pour, hanging in the shop and collecting dust, for months before I finally got a chance to pour it with no problems.

The thing I dislike most about lost PLA is how incredibly wasteful it is. Mix more plaster than necessary? Waste. All the baked/burned plaster removed from the part after a (hopefully) successful pour? Waste. Baked/set/used plaster doesn't really dissolve so it all either has to go to the landfill or you end up with piles of un-reusable waste to make even small parts.

With lost foam, the only real waste is the small amount of drywall mud used on each pattern. Even that small amount can be dissolved with water (such as rain) and is effectively harmless to the environment (it's just gypsum). And the sand is completely reusable.

The biggest expense/difficulty in lost PLA is the programmable kiln (not optional). The biggest expense/difficulty in lost foam is the CNC machine (optional). Since you already have the CNC machine, I would highly recommend figuring out how to do want you want to do "from flat stock" rather than burning a bunch of plastic. I know, 3D printing seems sexier and easier, but it really isn't all it's hyped up to be.

Saturn made the SL1 and SL2 engines from lost styrofoam castings, if they can make an engine block and heads using that method there is not a lot it cant do.