Hi;
Your cheapest and easiest bet is to purchase a couple Gluten-Free Cake mixes and when it says to add milk substitute it for either coconut milk (from a can), soy milk, hemp milk, almond milk, or rice milk, but I would first ask which milk substitute the person is used to using. They all have a very distinct and unique flavor, so stick with what they are familiar with.
Also be sure the mixes are dairy free before you purchase them. And 1 box only makes 1 single layer usually. Be sure to check. Pamela's is a good product.
I strictly bake & decorate Gluten-Free so I have on hand all the odd and unusual ingredients needed to make GF products. Unless you plan to make a lot of GF cakes I wouldn't buy all the individual ingredients, they can be very costly. The boxes of mix are expensive too but cheaper in the long run.
Also be very careful with cross contamination, it is a huge problem for those of us who are Gluten-Free.
Good Luck
You can PM me if you have any specific questions, be glad to help if I can.
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