That's a great looking car and the price (depending on condition) doesn't sound bad at all.
If you don't mind a long-winded reply, here's a list I assembled when I was Impala-shopping last year:
The bodies on 1965 and 1966 Impalas were rugged, but as with most 1960s cars, they are prone to rust. Steve Leuing, the National Impala Association and Vintage Chevrolet Club of America's technical advisor for 1965 full-size Chevrolets, says the biggest area of concern is body and frame rust. "Unfortunately, because of the nature of the construction of these cars, they are very prone to rusting in front, above and behind the rear-wheel opening, wheel wells, floors, trunk pan and gutters at the base of the windshield," Steve says. Convertibles are susceptible to severe rust in the front and rear floor pan because water doesn't get channeled out properly. However, one area of these cars, the rocker panels, remains solid unless exposed repeatedly to salt-covered roads. This is due to "flush and dry" rocker panels, which were designed to allow water to flow through, followed by a burst of air to dry out the remaining moisture. The door hinges were built like Fort Knox, but after 40 years, the bushings may need replacing.
Check for areas around the base of the front and back windshields, trunk pan, floor pans (especially around driver's side front).
The frames are strong, but rust attacks the "kick-up" area, where it goes up over the rear axle. Water and dirt collect, and rust starts. The frames also rust where the side rails meet the rear crossmember. Steve said, "The 1965 frames rust behind the front wheel where the boxed frame curves around and meets the straight part of the frame, just forward of the transmission crossmember. This area was very prone to collect dirt and water on the inside, resulting in the bottom of the frame rotting out over time."
Due to their size and weight, Impalas are known for wearing out lower ball joints, even with regular lubrication. The original ball joints were riveted on at the factory, so if you find a car with bolt-in type, they've been replaced. The upper ball joints, however, last nearly forever. The rear suspension is stout and has a rigid axle, coil springs, direct-acting shocks and a lateral control bar. Offered for the performance-minded driver was a heavy-duty suspension, which included a thicker front anti-roll bar, higher-rate springs, stiffer shocks, 14 x 6-inch-wide wheels and a redesigned rear stabilizer bar that attached to the lower control arms.
Make sure the frame is solid. Take a small hammer with you and tap on the entire frame from front to back. If it "rings", it's solid metal. If it sounds like you are hitting a rock, it's probably rusted through.
Areas to look at are the crossmember mounts on each side of the frame, especially before and after the rear axle hump. Check also for rust on the frame at the spring perch (drivers side), on trunk pans and around the bottom of the rear screen (caused by leaking rear screen).
The standard Impala interior included a bench seat with a combination vinyl-cloth material, which did not wear well. The dash was painted metal, but Chevy did offer a padded dash as an option. When new, 1965 and 1966 Super Sport Impalas included front bucket seats and an all-vinyl interior. The dash featured a brushed aluminum lower instrument panel, with a cluster including oil and ammeter gauges. The headliners, with the "star" pattern, were of much better quality than today's, and some originals have survived intact, with little wear; cars that have spent their lives in the desert, however, have headliners dry up from the heat. The original carpets are like anything else that wears when dirt and stones get embedded in the fiber. If kept clean, they hold up well. The all-vinyl seat covers were fairly tough, but after 40 years, the vinyl breaks down and begins to crack.