That’s right.
Here’s a concrete example. Let’s say that we have 256kB collations every 5 seconds per shard, that collations are notarised by committees of size 423, that each notary can only spare 0.5 Mbit/s of bandwidth to download collations, and that the notary deposit is 32 ETH. Then to activate a single shard we’d need at least 32 ETH * 423 * 256kB / 5s / (0.5 Mbit/s) = 11,089 ETH of deposits, or about 1.1M ETH for 100 shards.