Building your own scraper gives you the freedom to build it precisely how you want it to function. This also means that you’ll have full control over future updates and general upkeep of the tool. On the flip side, though, if you’re not the one who’ll do the building, you’ll need to have a dedicated person, which will result in bigger expenses.
Buying a scraper from third parties can be less expensive, but it also means spending more time on finding out which provider will best suit your needs. All in all, it all depends on your capabilities and what you need.