Buying anything always saves money in the long run. Wine making supplies are no different. However, you still need to mind some recipe items as they are perishable.
If you plan to use grapes, then you need to buy enough for the capacity you plan to make. Otherwise, the rest might go to waste. Yeast also does have expiry dates. To extend its longevity you need to keep it in a dry and cool environment. Pellets last longer compared to liquid yeast which runs for a few months of purchase.