Actually, that information is out of date (so if you could point me to it I’d like to see it so I can fix it). Now the cost is batch based. You can have an unlimited number of certs in a batch. Then the only cost you have to worry about is the transaction fee. If you want your transaction confirmed in a timely manner, that can be $1-2 USD lately. If you don’t mind waiting you can lower fees. (Bitcoin transaction fees in general are a much bigger issue I won’t get into here)
So in sum, the cost is independent of the number of certificates in a batch – there is only a transaction fee that you need to pay to have it processed.
In the future, other (non-Bitcoin) blockchain implementations will likely have different cost structures.