I want a good dairy cow under my budget.

For dairy, your budget is still too low for a good cow. A healthy Sahiwal, Gir, HF cross, or Jersey cross usually costs much more. If you want steady milk, look for a cow that is already milking in front of you, has a clean udder, and is in early lactation. Check all four quarters with a CMT test, and ask which month of lactation she is in, because a cow in late lactation will drop milk fast. If your budget is tight, it is better to wait and buy one good cow than to bring home a weak animal that gives little milk and more treatment cost.