Careful. Buying a used plane can be a money pit. How much do used 150s go for nowadays? $20K? You could easily sink that much into a used plane just bringing it up to safe airworthiness.
Yup they can be, but so can a newer one. I would rather start my money pit on the low end and work my way up. I just sold a airworthy 150 with less than 750 hours on the engine for $14,000. It wasn't the prettiest plane out there, but not bad at all and mechanically sound. Good cheap planes are out there, you just have to sort through the pile a bit and be patient.
Pete