"Cheap" should mean low cost to own, not just low sticker price. Plenty of £50 purifiers are false economy: tiny CADR, and proprietary filters that cost more than the machine within two years. The genuinely cheap route is high airflow through standard MERV-13 media.
Ready to clean up your London air?
Luggable MERV-13 kits deliver up to 681 m³/h CADR — built on the Corsi-Rosenthal principle, from £229. Ships from Oxford in 2–3 days.
Shop the UK store → See all kitsThe two truly cheap options
- Build a Corsi-Rosenthal box — £60–£120, unbeatable airflow per pound, a bit bulky and loud. Build guide →
- Buy a MERV-13 kit — from £229, quieter and tidier, filters from ~£58 a pair, no lock-in.
Running cost
The fans draw about 15W, so electricity is roughly £2 a year even running most of the day. Filters are the main ongoing cost, and standard MERV-13 media keeps that low. That's what ‘cheap’ should actually mean.
Why the £30–£50 units are false economy
The purifiers that fill the cheap end of Amazon look like a bargain and rarely are. Two things go wrong. First, the clean-air delivery rate is tiny — often well under 100 m³/h — so the unit cannot actually process the air in a real room quickly enough to matter. It hums away in the corner producing a reassuring light show and very little clean air. Second, most rely on small proprietary filters that need replacing every few months, and those cartridges quietly cost more than the machine within a year or two. You end up paying premium prices for commodity performance. "Cheap" in the honest sense means low cost to own across several years, not the smallest number on the box.
The genuinely economical route is high airflow through standard, inexpensive MERV-13 media. That is the principle behind both the DIY Corsi-Rosenthal box and the pre-built kits: move a large volume of air through good fine-particle filters that anyone can supply. MERV-13 captures roughly 93% of fine particles and, crucially, keeps airflow high, which is what clears a room. If you want the reasoning in full, our MERV-13 vs HEPA guide explains why throughput usually beats a fractionally higher single-pass rating at home.
What you actually pay over time
Break the cost into three parts and the cheap options look different. Upfront, a DIY box is £60–£120 and a Luggable kit starts around £229 (the 5-Fan, 369 m³/h CADR) rising to about £279 for the XL 7-Fan (681 m³/h CADR). Electricity is the easy part: the fans draw roughly 15W, so running one most of the day costs about £2 a year. Filters are the main ongoing line, and standard MERV-13 media — from around £58 a pair, lasting 6–12 months — keeps that low precisely because it is not proprietary. You can stock replacements on our MERV-13 filters page, and there is currently 10% off kits with code LONDON10, applied automatically through the store links.
Picking the cheapest option that works
- Tightest budget, don't mind bulk or noise: build a Corsi-Rosenthal box.
- Want quiet and tidy for the least sensible money: a MERV-13 kit sized to your room.
- Odours or cooking smells matter: choose a carbon-equipped kit, since particle filters do not remove gases.
Whichever way you go, the rule holds: judge on clean air delivered per pound over the machine's life. See the full field in our best air purifiers for 2026.
Frequently asked questions
What's the cheapest air purifier that actually works?
A DIY Corsi-Rosenthal box (£60–£120) offers the most clean air per pound. A MERV-13 kit from £229 is the cheapest quiet, tidy option once you count filter costs.
Why avoid £30–£50 mini purifiers?
Most have tiny CADR and rely on proprietary filters that quickly cost more than the unit. They can't clear a real room of PM2.5.