Have you ever made a bechamel with a non dairy milk?

I did this on Friday night with almond milk and earth balance margarine; it worked out fine. I have also had success with soy milk.
I would add to make sure you buy the "unsweetened" variety of whatever milk you use rather than the "original" variety. "Original" doesn't sound like it should be terribly sweet, but sometimes it is, and it makes a weird sauce. I find that almond milk in particular is naturally sweeter than its dairy counterpart. Try soy, or better yet, oat milk, if this offends your palate.

We're lactose intolerant, so we use unsweetened almond milk all the time. Makes a very acceptable bechamel.

+1 for using cashew cream
Soak cashews, i pour boiling water over, once it’s room temp to touch they’re good to go. Drain of water. Then blend together with salt, spices, a bit of lemon juice and add water to get the texture you want. For a cup finished cashew cream start with about 3/4 raw cashews. Must be raw cashews (not roasted) to get a smooth texture.
Works great for lasagna, or about anywhere you need a dairy free thick cream

I've used chicken stock as a sub for milk. I actually like it better than versions with milk. I've used it in lasagna and mac and cheese.

Awesome! Thank you Lori!

I've made bechamel sauce using soy milk and almond milk, both the unflavored kinds. I'm not vegan, but had family members taking antibiotics- which kind of eliminated dairy products. You don't have to make any adjustments as far as the amount of butter or flour, and both made tasty versions. In fact, I would say the almond milk version was one of my favorites. It brought an almost nutty underscore to the sauce, which you obviously don't get with regular milk. The soy milk version was also acceptable. I used the almond milk version for a lasagna, and the soy milk version for a "creamed" sauce for spinach. My family ate all of them and voiced no complaints. We are not vegan, so I did use butter- but I think you could easily use a vegan margarine without problems.