Desperate for a car under $6k: what's actually reliable?

At $6,000, you are shopping in a brutal zone. The price data for the Honda Civic and Toyota Corolla covers newer, far more expensive models, so you are looking at older examples than what the data describes. That means you must lean on known failure patterns, not typical resale values.

The Honda Civic is the riskiest pick here. Owner reports flag recurrent engine problems on specific generations that fall inside your budget: cracked engine blocks on 2006-2009 1.8L engines and head gasket failures on 2001-2005 D17 engines. Rust is also called out as recurrent on older generations, and the 8th generation (2006-2011) has notably poor paint and bad rear visibility. If you find a Civic, you are gambling on an engine that may already be compromised, and repair costs will blow past your budget fast. The only bright spot is that CVT failures are isolated, not widespread, but that does not offset the engine risk.

The Toyota Corolla has no reported issues in the provided data, which is a good sign, but the price range given starts at $16,069 for models from 2005 onward. That means a $6,000 Corolla will be older than 2005, and the data does not cover that era. You cannot assume it inherits the same reliability. Still, the absence of red flags in the data is meaningful, and Corollas are generally simpler cars. If you can find one with a documented timing chain or belt replacement and no accident history, it is your safest bet, but expect high miles and worn suspension bushings.

The Mazda 3 has no owner or price data provided at all. I cannot give you any factual reliability or cost information, so treat it as an unknown. Do not buy one based on reputation alone.

For your situation, the practical move is to hunt for a Toyota Corolla from the early 2000s with service records, even if it has 150,000 miles. Skip the Civic unless you are prepared for a possible engine swap. If no Corolla exists locally, widen your search radius by 100 miles. A known-good Corolla beats a cheaper unknown.