Milk is stored 25 to a barrel, and you don't cook it for food - make cheese out of it instead (kitchens have problem with liquids). You can cook the cheese if you want, its 5x the value of milk anyway.
Milk is definitely a good source of cheap food, and it processes extremely fast - 100 cheese is only 4 barrels of milk, which is 4 jobs which complete very quickly. Compared to buying meat you get 1/5 less barrels but have 2x the food. Say you want 50 food, buying 50 milk costs 50 points and gives 2 barrels. Buying 50 meat costs 100 and gives 5 barrels. Even if you outright bought the other 3 barrels for 10 each you would be saving 20 points. Plus the cheese is worth more in the end.
Brewing plump helmets saves a lot of money too. Again, you get fewer barrels, but you get much more wine. 100 wine costs 200 points from just buying it, and gives you 20 barrels. 100 wine from brewing costs 80 points and gives you 2 barrels and you also get a whole bunch of free plump helmet spawn. You could get the other 18 barrels if you really wanted by buying the wood for 3 points each and just making them on site and still be saving 33% of your points. Processing the plump helmets is also quick, but the barrels take a bit longer.
Another kinda cheaty way to supplement barrels is to just buy one of every animal type food. Meat or brains or whatever, just one from each animal. There are tons - you can get a barrel from buying a cave spider brain.
As far as what you would be saving these points to buy, I don't know - there isn't really anything in embark that you can't make yourself or import later.