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If you're quite set on the price range, I'd suggest you look at actual models. Take a look at ebay and maybe craigslist for used ones. Take a look at what is near your range new.

Apple laptops do seem to sell better even when they're old. This doesn't make them a good idea. Repairs are extremely expensive relative to what you will pay for one. If you're really looking to buy used, regardless of brand, do some research rather than focusing solely on price. I'd at least avoid any non business class Dells. They tend to suck.
 
Fix your Mac. I'd personally far rather use that over a Lenovo T61 (good business machine that it is) or the like which you'd get for the equivalent of $300 here.
 
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