Backup pricing comes in two shapes. One is a per-seat number. The other is a per-seat number plus an object-storage bill plus egress that becomes visible during a restore.
The second is not necessarily more expensive. It is unpredictable, which for an MSP is worse — you quoted the client a fixed monthly figure and the variance lands on you.
Egress is priced at the worst possible moment
Storage at rest is easy to model. Egress is not, because it is driven by incidents rather than by headcount, and incidents are exactly when nobody wants to be discovering a cost.
What bring-your-own-storage actually changes
Under BYOS the backups land in a bucket you own, in your own cloud account. The storage contract is between you and your storage provider. The backup vendor is not a party to it.
Three consequences follow, and they are all structural rather than commercial goodwill. The rate is one you negotiated, and it is on a bill you already receive. Nobody can change it without telling you, because nobody else is on the agreement. And the margin on that storage stays on your side of the table rather than being resold to you.
It also settles a residency question in one move: the data is in an account you control, in a region you chose, which is a materially easier thing to attest to a regulated client than a vendor's regional claim.
The trade-off, stated plainly
BYOS is not free of cost — it is free of markup. You take on a storage relationship: an account, a lifecycle policy, a bill to reconcile. For an MSP already operating in a cloud that is marginal effort. For one that is not, it is a genuine new responsibility.
The honest framing is that BYOS moves the storage decision to whoever is best placed to make it. If that is you, the model pays. If you would rather never think about a bucket, a bundled model is defensible — provided you have asked what a full restore costs, and got the answer in writing.
Who owns the bucket, and who sets the egress rate? Between them they determine whether a large recovery is a known cost or a surprise.