₹12,000 is a common air purifier budget in India. 9 of the 25 purifiers verified on this site fall below it, from ₹5,159 to ₹11,999, with a median of ₹9,299.
The number that matters here is CADR — Clean Air Delivery Rate, in m³/hr. It is how fast a unit actually clears particulate, and it is the only figure that compares two purifiers honestly. Across this page 6 of the 9 publish one, ranging from 152 to 350 m³/hr. A purifier rated for a room larger than yours is not wasted; it simply reaches clean air sooner and can then run slower and quieter.
Two of the 9 are CAR purifiers, which treat a car cabin and will not measurably clean a room. They are listed here because they genuinely cost less than ₹12,000, but do not compare them with the room units on CADR. 3 brands are represented: Honeywell 7, Levoit 1, Philips 1. Every price is the manufacturer's own, read from the brand's own store rather than a marketplace listing.
8 of the 9 carry HEPA media. Filters are the real cost of ownership — a HEPA and carbon set is roughly an annual replacement, so factor that in before choosing on purchase price alone.