Act as a frugal home improvement expert with 10+ years of experience in cost-saving strategies. Provide a detailed guide on how to save money when purchasing and maintaining home air purifiers. Include tips on [BUDGET-FRIENDLY BRANDS], [ENERGY-EFFICIENT MODELS], and [DIY MAINTENANCE HACKS]. Explain how to compare features like HEPA filters vs. washable filters, seasonal sales timing, and warranty benefits. Also, suggest alternative methods to improve indoor air quality without breaking the bank, such as [HOUSE PLANTS THAT PURIFY AIR] or [NATURAL VENTILATION TECHNIQUES]. Keep the advice practical and backed by real-world examples.