If you are looking purely to buy a Meal Replacement instead of making your own, then hands down the best one I have used is Major Mass by VMI. However, it does not contain Casein. Tastes amazing. However, if you have a good protein blend and just want to add Casein, then GNC Micellar Casein is a good cheap option, each scoop is 5g, so you can makeshift it as you need or see fit.
MRE is good, but it gets into the whole issue of protein sources and what Aminos are actually in there. NutraBio has MRP, which may be more in line with what you are looking for. @Kon_Rock is a rep and can probably get your more information if that is something you are interested in. Just my two cents!