You might have more luck if you post over at Classic Toy Trains forum, or the Model Railroader forum. Just click on either icon at the top of the page. Classic Trains forum is all about the real 1:1 scale.
As MOJAX says, the place to post this would be the Classic Toy Trains Forum. However, I can help you out here. Yes, it probably is worth it, but you probably aren’t getting that great of a deal. A 239 is generally only worth about $50 if it’s in nice shape. If the number on the cab is rubber stamped on (as opposed to heat-stamped) it is worth a bit more, though. If, however, it has a 234W tender (which includes a whistle, the number 234W will be stamped on the bottom), it would be worth about $100 and so you’d be getting a good deal then. Keep in mind that for vintage trains the overal cosmetic condition affects the value more than whether or not it runs.
Also, welcome to the O gauge toy train hobby! There are a lot of us Lionel guys over on the CTT forum who would be more than happy to give you all the advice you need to get started.