You did not say if your talking about an AOD or 5 spd car. I will assume an AOD since you state it comes out of drive.
If it is an AOD car I would first check to make sure your shift cable is adjusted correctly. Do you still have OD? I have been told OD is one of the first things to go on AOD's, as that is what happened to me. As far as buying or rebuilding what are you going to do with the car? If it's going to be a mostly stock daily driver I would check the classifieds here or craigslist.com to find a used / rebuilt AOD to get by. If you have extra money and are planning on building the engine I would buy a performance AOD from Lentech or Performance Automatic, or buy one of their high performance rebuild kits. However I am in the low 300 hp range with a stock rebuilt AOD I bought for $75 on craigslist.com and so far have made it last 2k hard miles. This is a great cheap replacement option until I have the cash for a HD AOD.
Now, if its a 5 spd do not waste your time or money having it rebuilt. (Unless you can do it yourself.) You will spend almost as much having a shop rebuild your stock one vs buying a completely new HD 5spd even if you have it rebuilt with a HD kit...I learned that from experience at the ripe age of 16.