They seem to run around $100-150 depending upon breed, age, production, health, etc.
Milk cow is considerably more expensive (maybe $800-ish), but the calves fetch a good price, so a healthy, weened calf might give a family an annual income of $300-400 per cow. But cows require more land and eat a lot more. But they put out more milk and can potentially make money.
Chickens can also provide eggs and offspring for sale. A dozen chickens and a rooster who takes care of business can go a long way to keeping a family alive and makes a small income to boot.
Lots of different possibilities.