Quick answer
If you need a small bedroom air purifier for allergies under $200, start with a unit that has a smoke CADR around 90 CFM or higher for a 130 sq ft room, a quiet low setting you can sleep through, and easy-to-find replacement filters. For most bedrooms, the Levoit Core 300S is the safest compact pick, the Coway Airmega 150 is the nicer step-up if it is on sale, and the Levoit Vital 100S is a practical choice when you want a washable pre-filter and pet-hair-friendly front intake.
An air purifier will not fix the source of pollen, dust mites, pet dander, or mold, and it should not replace medical advice or moisture control. What it can do well is keep airborne particles moving through a filter all day, which is exactly what a small bedroom needs during allergy season.
How much purifier does a small bedroom need?
For allergies, do not buy from the giant square-foot number printed on the box. Those claims are often based on one air change per hour, which is too weak for allergy control. A better shortcut is to look at CADR, especially smoke CADR, because it gives you a cleaner comparison across brands.
For a 130 sq ft bedroom with an 8 ft ceiling, a purifier with roughly 90 CFM of CADR is the minimum I would consider. Models around 140-160 CFM give you more headroom, which matters because you probably will not run the purifier on its loudest setting while sleeping. Bigger is fine as long as the low and medium settings are quiet.
Best first pick: Levoit Core 300S
The Levoit Core 300S is the easiest recommendation for a small rented bedroom because it is compact, widely available, usually priced around $130-$160, and strong enough for the room size. Levoit lists the Core 300S-P at 141 CFM / 240 m3/h CADR with a 22-50 dB noise range, which is a good fit for a dorm room, student apartment bedroom, or small home office.
The round design is simple to place, the app and auto mode are nice extras, and replacement filters are easy to find. The tradeoff is that round filters can get pricey if you buy branded replacements, so check the annual filter cost before you decide that the cheapest sale price is the best deal.
Better if it is on sale: Coway Airmega 150
The Coway Airmega 150 is usually closer to the top of the $200 budget, but it is worth watching when discounts bring it down. Coway lists the Airmega 150 with CADR ratings around 153 for smoke, 161 for dust, and 220 for pollen, plus a washable pre-filter and separate deodorization and HEPA-style filter stages.
This is a good pick if you want a more traditional rectangular purifier that looks less like a gadget and has a pull-out pre-filter that is easy to clean. It is also a sensible option for pollen-heavy rooms because its pollen CADR is strong for the size. The downside is that it is not always the cheapest, and filter availability can vary more by retailer than Levoit.
Good for pet hair and dust: Levoit Vital 100S
The Levoit Vital 100S is another strong under-$200 bedroom option, especially if dust and pet hair are part of the problem. Its front intake and washable pre-filter make it easier to keep lint and hair from loading the main filter too quickly. Published specs put it in the same general CADR class as the Core 300S, around 141 CFM / 240 m3/h.
It is not as compact as the Core 300S, so it needs more wall or floor space. But if the purifier will sit near a bed, litter area, closet, or dusty corner, the easier pre-filter access can matter more than the smaller footprint.
What about Blueair and Winix?
Blueair's Blue Pure 511i Max is quiet, compact, and attractive, and it can make sense for a tiny bedroom where noise and design matter most. Just know that Blueair uses its HEPASilent approach rather than the same style of sealed true-HEPA design some allergy buyers specifically look for. That is not automatically bad, but it is worth knowing before you buy.
Winix models like the 5500-2 are often excellent values, but they are physically larger and more living-room-sized than a student bedroom usually needs. If you find a sale around $150 and have the space, a larger Winix can be a good deal. For a 130 sq ft bedroom, it may simply be more machine than necessary.
Setup matters as much as the model
Put the purifier in the room where you sleep, not in the hallway. Keep the intake and exhaust unblocked. Run it continuously on medium when you are out of the room, then low or sleep mode at night if noise bothers you. During heavy pollen days, keep windows closed and change clothes or shower before bed if you have been outside for a while.
If mold is part of the concern, a purifier can catch airborne spores, but it cannot solve damp materials or humidity. Keep indoor humidity roughly in the 40-50 percent range when possible, fix leaks, and treat visible mold as a source problem.
Bottom line
For a small bedroom under $200, I would buy the Levoit Core 300S first if you want the easiest all-around choice. I would choose the Coway Airmega 150 if it is discounted and you want a stronger, nicer-feeling unit. I would pick the Levoit Vital 100S if dust, lint, or pet hair are a big part of the room's air problem. In all three cases, the right size, continuous use, and affordable replacement filters matter more than smart features.