Firstly, you are unlikely to get something that is truly an antique unless you can get it appraised by a specialist and buy the statue at an auction house. So you are more than likely to end up wasting your money.
And if you ARE able to find an authentic antique statue, then unfortunately it is probably stolen. Just think of all the bad karma you are likely to enjoy by purchasing a stolen statue.
Theft of Buddhist images is rampant in many parts of Asia, and the forces that drive that theft are people who are looking to buy an antique rupa (a carving of the Buddha). Temples in Thailand, Cambodia and Laos are often robbed of their images, some of them several centuries old. These statues are often venerated by the Buddhist population in the village. They mean more than just a religious icon; to the neighboring laypeople who go to this temple, they would have a particular veneration for that Buddha statue.
And many villages and towns are KNOWN by the statues in their local temples. For instance, my home town of Phitsanulok, Thailand is know for the Chinaratra Buddha statue enshrined at Wat Mahathat. If that statue were to be removed, then a significant amount of tourism would be lost to the town, since so many people from all over Asia travel to that temple to pay homage to the statue there.
In short, the whole economy of a village or town can be affected when a statue is stolen and sold on the black market. (See Also: Golden Buddha Statues Stolen From Thai Temple )
If you travel to the town of Ayutthaya in central Thailand, a city that is loved for its ancient ruins, you will see many stone statues outside the old temple walls that are missing a head. Those statues were decapitated since the thieves couldn't steal the whole (life-size) statue of the Buddha, instead they broke off the head and sold that on the black market.
If you have a hard time relating to this, then think of it this way; what if many of the beautiful Christian works of art found in Rome and churches throughout Italy were stolen and ended up in the homes of wealthy NON-Christians?
So in short, stay away from antique statues unless you are interested in either buying a fake, or contributing to the ransacking of Buddhist temples and cultural sites throughout Asia.