I wouldn't recommend it. Not only are many a sham, $30/mo isn't likely to buy you many bottles of interest. I think you'd be better off just buying a case of their favorite wine.
That said, if you are really interested, you might want to seek out a local wine club. Most cities have a group of wine enthusiasts that put together recommended bottles every month or so. The bigger clubs will actually buy the bottles and make them available for pick-up. It has the added bonus of being able to discuss these bottles at the wine clubs if your parents are so inclined.
That's my take.