I want to buy a cow under my budget.

For a dairy cow, first fix your budget and then shortlist Sahiwal, Gir, HF cross, or Jersey cross. Before paying, milk her in your presence, do a CMT test on all four quarters, ask the lactation month, and check age and body condition. If you want steady fifteen liters or more, one cow is not enough; you need two with staggered calvings. For any cow above fifty thousand rupees, take a Pashumitra or vet with you.