I need a cheap, reliable used car under $10k for a daily commute of 40+ miles. Fuel economy and low maintenance are key. What should I buy?

For a cheap, reliable used car under $10k with good fuel economy and low maintenance for a 40+ mile daily commute, the Honda Civic is the only candidate with enough data to consider, but it comes with notable risks. The Toyota Corolla is priced out of your budget, its typical used price ranges from $16,069 to $24,220, well above $10k. The Mazda 3 has no owner data or price info available, so it cannot be evaluated.

The Honda Civic has a typical used price of $16,723 to $27,952, which also exceeds $10k for most models. If you find one under $10k, it will likely be an older generation with known issues. The 7th generation (2001-2005) has recurrent head gasket failures on the D17 engine, and the 8th generation (2006-2009) has isolated but severe cracked engine blocks on the 1.8L R18 engine. These are expensive repairs for a long commute. The 1.5L turbo engine in newer models has recurrent oil dilution problems, especially in cold climates, though a software update helped. The CVT transmission has isolated long-term reliability concerns. Rust is recurrent on older Civics, requiring undercarriage care. Paint quality on the 8th generation is poor, and visibility can be bad due to blind spots.

For your situation, under $10k, high mileage commute, low maintenance, the Civic is not ideal. The engine and transmission issues on older models could lead to costly repairs that outweigh fuel savings. You would be better off looking at other reliable, fuel-efficient cars that fit your budget, like a used Mazda 3 (if data becomes available) or a Hyundai Elantra, but based on the provided data, no candidate here meets your needs reliably. Stick to cars with a proven track record under $10k, like a 2010-2014 Honda Fit or a 2012-2016 Toyota Yaris, which are cheaper and have fewer major issues.